From your fact check source, Millgirl.

“The report said that more than 32,000 migrant children failed to appear for scheduled court hearings during that period. Also, 291,000 more children as of May 2024 did not receive a "notice to appear" in court from Immigrations and Customs Enforcement, so did not yet have an immigration court date. Together that’s about 323,000 children.

The report does not describe those children as missing, but said children who don’t appear in court are considered "at higher risk for trafficking, exploitation, or forced labor." The 32,000 figure could be higher, the report said, because of the agency’s failure to issue "notices to appear" to 291,000 children.