Activists planning to line California roadways with anti-vaccination billboards full of misinformation are paying for them through Facebook fundraisers, despite a platform-wide crackdown on such campaigns.

According to organizers, the billboards will feature the faces of two children whose parents claim were killed by vaccines, though the claims are contrary to medical evidence. Catelin Clobes, the mother of one of the pictured children, raised $16,304 for the campaign through 491 Facebook users and says the funds have paid for billboards in Modesto, Sacramento and Merced, the first of which is set to go up this month.

The billboards will include the website address for the Informed Consent Action Network, the nation’s best-funded anti-vaccination group. Del Bigtree, the former daytime television producer who leads the group, told NBC News he was unaware of the campaign.

Clobes’ fundraiser is one of dozens on Facebook that have raised money recently for anti-vaccination campaigns and nonprofits, despite the company’s announcement in April of a restriction on vaccine misinformation fundraising. At least $27,000 has been raised on Facebook in the last six months for such efforts.

Recent campaigns have funded billboards and bus signs, organized anti-vaccination events and paid for the maintenance of what’s known as the “Vaxxed Bus,” an RV emblazoned with the title of an anti-vaccination documentary that prominent anti-vaccination activists used to travel on a nationwide tour.

The fundraisers underscore the challenge of content moderation on Facebook’s massive scale, where hundreds of millions of people post billions of times each week. While Facebook’s crackdown halted fundraising for the biggest anti-vaccination groups on the platform, smaller groups and individual fundraisers have fallen through the cracks, NBC News found.

Facebook responded to questions from NBC News about several active anti-vaccination campaigns by closing one fundraiser, but many remain.

"We partner with leading public health organizations, such as the World Health Organization and the U.S. Centers for Disease Control and Prevention, which have publicly identified verifiable vaccine hoaxes,” a Facebook spokesperson wrote in an email to NBC News. “If these vaccine hoaxes appear on Facebook, we will take action against them, including the removal of access to our fundraising tools."

Public health officials say the science on vaccines is clear: They are both safe and essential to protecting the health of vulnerable populations, including infants and the elderly. The ideas promoted by anti-vaccination groups — which rely on pseudoscience and conspiracy theories about the government and pharmaceutical companies — are false.

The current anti-vaccination movement was built on Facebook and other social media platforms, as well as crowdfunding sites, which spread their message and financed their various campaigns. But in recent months — amid rising concern over vaccine hesitancy and the worst measles outbreak in decades — the platforms that amplified and funded a conspiracy movement have taken steps to muzzle it.

Following similar decisions by Pinterest and YouTube, Facebook announced in March that it would limit the reach of anti-vaccination content, no longer serve up anti-vaccination groups and pages in search results and the recommendations bar, and stop accepting ad buys from users and groups that spread vaccine misinformation. Then, in April, after GoFundMe and Indiegogo both banned anti-vaccine campaigns, Facebook widened its anti-vaccination restrictions to include fundraising.

Facebook soon removed the largest anti-vaccination groups from its list of nonprofits eligible to receive fundraising donations. In 2018, prominent anti-vaccination activist Robert Kennedy’s Children's Health Defense fund raised $30,000 on the platform, and a month before Facebook’s announcement, activist Brandy Vaughan raised more than $8,000 for a billboard campaign from her anti-vaccination group, the Council for Vaccine Safety. Today, both groups are no longer listed among Facebook’s eligible nonprofits.

The donation pages for other anti-vaccination groups that once raised funds through Facebook, including Bigtree’s Informed Consent Action Network and Physicians for Informed Consent, currently read, “This content is no longer available.”

While the largest anti-vaccination groups have been effectively cut off, smaller individual activists who make up the movement have responded with creative workarounds. Many have continued to host fundraisers through the platform, concealing the nature of their campaign to evade Facebook’s enforcement, swapping the word “vaccines” for terms like “medical freedom” or “informed choice.” Other groups, including National Vaccine Information Center, the country’s oldest anti-vaccination nonprofit with more than 218,000 Facebook “likes,” have used outside services that manipulate Facebook’s layout to include custom donation tabs on their page.

“The harder platforms go with bans, the harder users will go to circumvent those bans,” said Ysabel Gerrard, a lecturer at the University of Sheffield’s Department of Sociological Studies, who researches content moderation and sits on Facebook's Suicide and Self-Injury Advisory Board.

Evading moderators “becomes a pleasurable cat-and-mouse game,” Gerrard said. “Communications become more insular and more niche, and you add a new level of pleasure when you ban something.”

“The people who are really hardcore into a community will evade bans,” Gerrard added. “But moderating hopefully restricts new people from finding the community.”

Six personal fundraisers on Facebook are currently raising money for First Freedoms, a nonprofit led by the author of a prominent anti-vaccination book that falsely alleges vaccines are dangerous and the CDC has conspired with pharmaceutical companies and the American Academy of Pediatrics to keep that information from the public.

First Freedoms has raised thousands of dollars on the platform in recent months for a campaign to keep religious exemptions to vaccines intact in New York State. Its page is loaded with videos that push vaccine conspiracies, including that the CDC over-hypes measles outbreaks to scare the public and that New York’s exemption legislation is fueled by an “unholy alliance between the pharmaceutical industry and government.”

The fundraiser that Facebook closed after NBC News’ questions was on behalf of the anti-vaccination group Informed Choice Michigan, which was using Facebook to fund an upcoming event. “The V word was never even used in any of the posts we made to the fundraiser!” the page’s administrator wrote. “Censorship is real people!”

In an email to NBC News, Facebook said the fundraiser violated policies unrelated to vaccines.