The US health department has received more than 4,500 complaints of sexual abuse against detained migrant children from 2014-2018, documents show.
The Department of Justice reportedly received an additional 1,303 sex abuse complaints against unaccompanied minors during the same period.
Congressman Ted Deutch, who released the figures, said at least 154 claims are against facility staff members.
A spokesman for the health department said it takes the claims seriously.
"These documents demonstrate over the past three years there have been 154 staff-on-unaccompanied-minor - let me repeat that, staff-on-unaccompanied-minor - allegations of sexual assault," Congressman Deutch said during a House Judiciary Committee hearing.
The hearing, which focused on the Trump administration's "zero tolerance" immigration policy that led to thousands of immigrant children being separated from their families, featured testimony from Jonathan White, the deputy director for children's program's at Health and Human Services' (HHS) Office of Refugee Resettlement (ORR).
"This works out, on average, to one sexual assault by HHS staff on an unaccompanied minor, per week," Mr Deutch continued.
Mr White clarified that those allegations are not against HHS staff, but rather against the contractors who are paid by HHS to run the underage migrant detention facilities.
"I will make that clarification. It doesn't make what happened any less horrific," Mr Deutch responded.
Caitlin Oakley, a spokeswoman for HHS, said the shelters are run by childcare service centres that are licensed by state officials.
"These are vulnerable children in difficult circumstances," she said in a statement to Axios, which first reported the documents.
"When any allegations of abuse, sexual abuse, or neglect are made, they are taken seriously and ORR acts swiftly to investigate and respond."
The allegations include sexual relationships, showing pornographic videos to children and forcible touching, according to Axios.
The figures were revealed as Democrats on the House Committee on Oversight and Reform voted to issue subpoenas to Trump administration officials involved in the now-suspended policy of separating parents from their children after they illegally cross the US-Mexico border.