The post contained a video clip, from an interview with Fox & Friends earlier in the day, in which Trump claimed that children are "almost immune" to COVID-19.
"This video includes false claims that a group of people is immune from COVID-19, which is a violation of our policies around harmful COVID misinformation," a Facebook spokesman said.
A tweet containing the video that was posted by the Trump campaign's @TeamTrump account and shared by the president was also later hidden by Twitter Inc for breaking its COVID-19 misinformation rules.
A Twitter spokesman said the @TeamTrump account owner would be required to remove the tweet before they could tweet again.
YouTube, through a spokesman, said it had also pulled down the video for violating its COVID-19 misinformation policies. However, the original interview remains available on the Fox News page on the platform. YouTube did not immediately respond to requests to clarify which videos were taken down.
The Trump campaign accused the companies of bias against the president, saying Trump had stated a fact. "Social media companies are not the arbiters of truth," said Courtney Parella, a spokeswoman with the campaign.
The Centers for Disease Control and Prevention (CDC) has said that while adults make up most of the known COVID-19 cases to date, some children and infants have been sick with the disease and they can also transmit it to others.
An analysis by the World Health Organization of 6 million infections between Feb. 24 and July 12 found that the share of children aged 5-14 years was about 4.6%.
The White House did not immediately respond to a request for comment. During a briefing at the White House, Trump repeated his claim that the virus had little impact on children.
"Children handle it very well," he told reporters. "If you look at the numbers, in terms of mortality, fatalities ... for children under a certain age ... their immune systems are very very strong and very powerful. They seem to be able to handle it very well and that's according to every statistical claim."
It was the first time Facebook had removed a Trump post for coronavirus misinformation, the company's spokesman said.
It also appeared to be the first reported instance of the social media company taking down a post from the president for breaching its misinformation rules.
Twitter has taken down a post retweeted by Trump pointing to a misleading viral video about the coronavirus, but left up clips of the president suggesting scientists should investigate using light or disinfectant on patients.
Twitter said those remarks expressed a wish for treatment, rather than a literal call for action.
It also left up a March post from Tesla Inc's outspoken CEO Elon Musk stating that "kids are essentially immune" from the virus.
Facebook has taken heat from lawmakers and its own employees in recent months for not taking action on inflammatory posts by Trump.
The company has previously removed ads from Trump's election campaign for breaking misinformation rules, in that case around a national census.It also took down both Trump posts and campaign ads that showed a red inverted triangle, a symbol the Nazis used to identify political prisoners, for violating its policy against organized hate.