On May 1, 2025, a young mother in a small Idaho town said she found her twin toddlers dead in their bed, cold and lying on their bellies.

Three days later, she sat for an interview with Children’s Health Defense, the anti-vaccine nonprofit co-founded by Health Secretary Robert F. Kennedy Jr., claiming that vaccines caused their deaths. The story was sensational, billed on the group’s website as “breaking news” of toddlers who were born together and died together, “FOLLOWING VACCINATIONS.”

The organization quickly embraced the woman, Andrea Renee Shaw, naming her the lead plaintiff in two legal actions against the nation’s top society of pediatricians claiming that the organization, the American Academy of Pediatrics, lied about the safety of childhood vaccines.

Then, last week, after a nearly 14-month investigation by the Payette Police Department, a grand jury indicted Ms. Shaw, 23, on charges of murder, claiming that she suffocated the children in an act that was either premeditated or taken in the course of aggravated battery.

The police and the county prosecutors did not release details about the evidence or return calls from The New York Times. “This arrest is the result of a lengthy and thorough investigation conducted by the Payette Police Department, with invaluable assistance from numerous partner agencies,” the police said in a brief statement, adding that the Idaho State Police Forensic Services and the Boise Police Department were among the agencies that assisted.

Neither Ms. Shaw nor Children’s Health Defense are backing down from their claim that vaccines killed both children.

Ms. Shaw’s lawyer, Joseph Filicetti, said in an interview on Tuesday that he would argue that vaccines caused the suffocation. Experts say there is no evidence that vaccines can cause suffocation.

Mary Holland, the Children’s Health Defense chief executive, said the group planned to stand by Ms. Shaw’s claim.

“They’re messing with the wrong people,” Ms. Holland said on a broadcast on the group’s website after the indictment was made public. She added: “We stand for the truth, and the truth is, that vaccines can cause death, and there’s zero evidence so far that this woman killed her children, zero.”

The latest cause célèbre of Children’s Health Defense underscores the intensity of the organization’s drive to raise questions and fears about the safety of common childhood vaccines through the stories of grieving parents whose children’s deaths have not been fully explained.

The Shaw case appears to be part of a pattern of cases in which vaccine activists have stood behind parents who may have played a role in a child’s death but claimed instead that vaccines were the culprit, said Dorit Reiss, a professor at the University of California College of the Law, San Francisco, who specializes in vaccine law and policy.

“Notice that they’re doubling down, they’re not stepping back, and they’re not giving up,” said Ms. Reiss. “In their alternative reality, this is more evidence that vaccines are not safe, and the system is trying to cover it up.”

Mr. Kennedy has not spoken publicly about the Shaw case but he advanced similar claims as a vaccine activist leading the group, suggesting during the early rollout of Covid vaccines that the shots killed the baseball legend Hank Aaron and were behind a “wave of suspicious deaths.” Mr. Kennedy also used the nonprofit’s social media channels to recruit plaintiffs for a lawsuit against a vaccine maker.

In an interview Tuesday, Ms. Holland, the leader of Children’s Health Defense, did not answer questions about how the nonprofit connected with Ms. Shaw three days after the toddlers died.

“It’s not unusual at all that in a case like that we would be alerted,” she said. “We’re probably the only organization that would take a case like that very seriously and put out information about it right away.”

When she appeared on the group’s broadcast three days after the deaths, Ms. Shaw described finding her fraternal twins, Dallas and Tyson, on their shared bed, their faces frozen as if they remained asleep. Her husband, Nathaniel Shaw, cried during the interview, recounting his son and daughter as caring, mellow and smart toddlers.

“Her smile, you could see it and it would make the sun just seem dim,” Mr. Shaw said, describing his daughter Dallas. “It could just light up your whole world as nothing else ever could.”

Ethan Mittelstadt, the Payette County coroner, said the autopsy records would not be available until the criminal case was resolved.

During the Children’s Health Defense broadcast, Ms. Shaw said the toddlers were born prematurely at 29 weeks, but had thrived in their small community about 60 miles north of Boise. She said that she had gotten them most of their recommended shots and that they had no problems with any vaccine until late in April 2025. On April 23, she said, they had several vaccines and the following day developed diarrhea and lethargy, prompting her to take them to an emergency room. They were discharged within hours, she said.

Hospital records provided by Children’s Health Defense show that one of the children had a fever of 99 degrees. The doctor deemed them to have had a “post-immunization reaction” that was treated with Tylenol and ice pops.

They died eight days after they got the vaccines — a shot for hepatitis A, another for flu, and a third for tetanus, diphtheria and pertussis, she said. She recounted in the interview that during the second day of police questioning her about the toddlers’ deaths, officers suggested that she was to blame.

“They said that it wasn’t medical,” Ms. Shaw said during the Children’s Health Defense interview. “And that they figured asphyxiation, and that I had supposedly had a postpartum overwhelming blackout, and done it to my children.”

Polly Tommey, a programming director for Children’s Health Defense who interviewed the couple, appeared to lead them in the interview to disavow vaccines, saying, “We have to warn the people of these vaccines.”

She asked: “You’re so pro-vaccine, so how does that make you both feel that this has happened, that you were lied to?”

“I feel that I wish I was anti-vaccine now,” Ms. Shaw said.

Ms. Shaw’s lawyer said she was arrested last week, five days after giving birth to another child. She remains in jail, unable to provide the $2 million bond for her release.

“She’s absolutely denied throughout all the interviews and continues to deny that she did anything,” Mr. Filicetti said, adding: “This gal is the kindest, sweetest, gentlest person I’ve ever met. I mean, she never even had a parking ticket in her life.”

He said the main issue in the case would be whether Ms. Shaw or the vaccines caused the suffocation.

Dr. Peter Hotez, a vaccine expert at Baylor College of Medicine in Texas, said the theory lacks plausibility, especially given that both children, who were not identical twins, died at about the same time more than a week after vaccination.

“I’m not aware of any vaccine that would be able to cause suffocation,” he said, adding. “If that were the case, you’d expect to see other cases appearing in the community.”

In January, Ms. Shaw became the lead plaintiff in a Children’s Health Defense lawsuit accusing the American Academy of Pediatrics of “racketeering,” which is defined as gaining money through “illegal enterprise usually involving intimidation.”

The case, which is pending, rests on the notion that Ms. Shaw and others were victims of the A.A.P., which Children’s Health Defense said falsely claimed that vaccines were safe.

Backing a motion to dismiss the case in a court filing, the pediatricians group said: “Accusing people you disagree with of being criminal racketeers — and at the expense of children’s lives no less — is beyond the pale and a profound abuse of the legal system.”

Children’s Health Defense also tapped Ms. Shaw as the lead plaintiff in an effort to intervene in a lawsuit the pediatrician’s group has brought against Mr. Kennedy. That case is focused on Mr. Kennedy’s decision as federal health secretary to dismiss the members of a prominent vaccine advisory group and replace them with people with few qualifications, many of whom have raised concerns about vaccines.

Children’s Health Defense and other groups filed an “emergency motion” to join the case to “speak for the children who have been injured or who have died from the vaccines,” based on the pediatrician group’s guidelines.

The judge rejected Children’s Health Defense’s motion to intervene.

As nicotine pouches explode in popularity, tobacco companies are investing heavily in factories in the United States and creating new jobs from Florida to Colorado.

Along with vaping products, the Big Tobacco corporations have seized on the nicotine pouch market as a way to offset the steep decline in domestic sales of cigarettes. Pouch sales are projected to increase to more than $40 billion worldwide by 2033 from $6.9 billion in 2025, according to an analysis by Grand View Research, a market research firm.

Companies are racing to meet the demand, so far investing more than $1 billion in plant production to accommodate the growth. Several states have welcomed the industry’s forays into the latest twists on nicotine products, handing out millions of dollars in tax credits and grants.

But the marketing of nicotine-laden items like pouches, gums and lozenges as another safe alternative to traditional cigarettes has heightened public health concerns. Experts are accusing the tobacco industry of once again deliberately ignoring decades of science that proved the addictive nature of nicotine, and of stoking demand by producing more and more potent varieties.

Reminiscent of Juul and other flavored vaping products that caused a public uproar over teenage consumption, the pouches — tobacco-free “lip pillows” placed between the cheek and gum — have revived warnings that nicotine is highly addictive and can cause a host of conditions, like anxiety and heart arrhythmia. It also threatens a teenager’s still-developing brain, with the potential for affecting behavior and cognitive function, experts say.

Colorado’s governor, Jared Polis, a Democrat, defended his state’s decision to support a new $600 million plant in Aurora, built by Philip Morris International, which is getting $4.5 million in state tax credits.

“We were the first state to legalize marijuana, and now have over 650 dispensaries, have legalized natural medicine and have almost 50 regulated healing centers that offer psilocybin,” Governor Polis said. “Of course, we want safer alternatives to smoking, like Zyn, to be in our state.”

The expansions signal the tobacco industry’s influence in the widening debate over the safety of this new generation of products.

As a major donor to President Trump, the industry has enjoyed a friendlier reception from his administration than they did from other presidents.

In May, the Food and Drug Administration issued new guidance relaxing regulations on nicotine pouches and vapes, a week after the tobacco company Reynolds American donated $5 million to a Trump-backed super PAC.

In late June, the F.D.A. announced that it would allow some products from one brand, Zyn, to be marketed as having a lower risk for some cancers and diseases than cigarettes do.

The pouches also have a prominent booster in Robert F. Kennedy Jr., the U.S. health secretary, who has described pouches as “probably the safest way to consume nicotine” and has acknowledged using them.

Zyn is produced by Swedish Match, a Philip Morris International subsidiary. Its plant in Aurora employs more than 120 people, with plans to expand to 500 employees. In addition, the corporation spent $232 million to build a plant in Owensboro, Ky., and employs 340 workers there.

In the last two years, Reynolds added about 1,000 jobs in the United States, mainly through pouch-making expansion, according to Luis Pinto, a company spokesman.

Altria, which makes Marlboro cigarettes, is producing the brands called on! and on! PLUS in Richmond, Va. The company won F.D.A. approval in December for additional pouch products under a new streamlined program. (Altria was known as Philip Morris, which rebranded in 2008 and spun off international sales to Philip Morris International.)

In December, Swisher, known for Swisher Sweets cigars, announced a $135 million expansion to its Jacksonville, Fla., factory. The company said it expected to add at least 240 jobs to support production of nicotine and caffeine pouches.

And the Swedish firm WiJo is spending $13 million to open its first pouch plant in North America, in Lexington, S.C.

In South Carolina, a large Juul plant in Lexington County that had been awarded tax abatements and grants closed after a federal ban on most flavored vapes in 2020, and politicians said they were glad to see it go. But officials in the same county awarded tax incentives to WiJo for its pouch factory last year.

The American tobacco industry has imported the technology for nicotine pouches from Sweden, often by purchasing that country’s companies. Altria bought Helix Sweden in a series of deals starting in 2019. Philip Morris International bought Swedish Match for $16 billion in 2022.

Garrett Nelson, a senior equity analyst at CFRA, said smoke-free nicotine products like pouches and vapes were generating new revenue for a tobacco industry that had appeared moribund.

“They are now viewed as growth companies, and there is a lot of optimism surrounding products like Zyn and IQOS and other smoke-free products,” Mr. Nelson said in an interview.

Zyn dominates the pouch market.

“If you look at the first quarter, they have 61 percent retail market share in dollar terms of the nicotine pouch market in the U.S. and, on a volume basis, about 56 percent of the market share,” Mr. Nelson said.

While most of Philip Morris International’s revenue continues to come from cigarettes, Zyn has helped the company to nearly double its share price in two years.

But the supposedly safer alternatives to traditional smoking haven’t quelled concerns about nicotine dependence. Symptoms include irritability, restlessness, trouble concentrating, anxiety, and appetite and mood changes.

The American Lung Association has sounded the alarm about pouches becoming the latest avenue for young people to develop an addiction. Citing similar concerns, in May the World Health Organization urged stricter regulation of them. In April, France went further by outlawing nicotine pouches, causing trade tensions with Sweden.

Sam Dashiell, a spokesman for PMI, disputed claims that these products targeted young people, saying pouches were being marketed to the 25 million adult Americans who still smoked cigarettes.

“Smoke-free products are a better option for current legal-age nicotine consumers who would otherwise continue smoking or using other traditional tobacco products,” Mr. Dashiell said.

Pouch proponents often cite the success in Sweden, where smoking rates have dropped considerably, and where the switch from cigarettes to pouches is sometimes called “the Swedish model.”

These products use nicotine extracted from tobacco leaves or synthetic nicotine, which is becoming more common. The pouches contain a powdered mix of nicotine, flavors and other ingredients that dissolve in the mouth.

Pouches are often promoted as more than a cigarette replacement. Some MAHA-aligned health influencers (a.k.a. Zynfluencers) endorse them as a hack for energy and cognitive enhancement. The conservative media host Tucker Carlson, who co-owns a pouch brand, promotes pairing nicotine and caffeine products “for a perfect coffee break.”

Mr. Dashiell said Phillip Morris International does not pay social media influencers to market its pouches.

Dr. Gina Kruse, a professor of medicine at the University of Colorado Anschutz who researches tobacco cessation, said more research was needed to determine the effects of nicotine pouches.

“A lot of the studies that have looked at things like the cytotoxicity of pouches, or the constituents, have come from industry,” she said. “And there’s an urgent need for more independent research to understand what risks come with these.”

She added that a broad concern centers on the potential for pouches to become an “on-ramp” to nicotine dependence, and entice people to move to harmful products like cigarettes. “And there’s certainly concern about flavors appealing to youths,” Dr. Kruse said.

A growing worry is that companies are raising the levels of nicotine, making the pouches more potent and more addictive, said Sven Jordt, a distinguished professor at Duke University School of Medicine.

Dr. Jordt, who is a member of the F.D.A.’s advisory committee on tobacco products, said the highest levels of nicotine in some popular pouches had risen from six to eight milligrams of nicotine per pouch to nine to 15 milligrams. “That’s definitely a quantum jump.”

The stronger pouches include Reynolds American’s Grizzly and Velo Plus, and Philip Morris International’s Zyn Ultra, he said.

“We need to investigate what happens in long-term use, to the whole digestive system,” he said.

“It’s another source of artificial sweeteners, with their own issues,” Dr. Jordt added. “What happens to sleep behavior, what happens to fertility? There have to be studies about oral health — how does it affect gum health?”

Dr. Jordt said Sweden was a cautionary tale: “Now they have an epidemic of oral tobacco use, and I think that might, unfortunately, be the future in the United States.”

The expansion of factories “signals the strategies of these companies for the future,” he said.

Mr. Pinto of Reynolds American said the company planned to spend $3.2 billion by 2030 to make more nicotine products, with pouches driving most of the expansion.