Migrant children detained at the border continue to sleep in cold cells without proper clothing or adequate food, a top Democratic lawmaker said on Thursday, accusing the Department of Homeland Security of blocking members of Congress from visiting the facilities.

Parents were not provided enough diapers for their children, toddlers were fed “burritos rather than age-appropriate foods” and one child was told by an immigration agent to eat food off the floor, according to interviews that House Democrats conducted with detainees during earlier visits.

In a letter sent on Thursday to Kevin K. McAleenan, the acting secretary of homeland security, the chairman of the House Oversight and Reform Committee, Representative Elijah E. Cummings of Maryland, said poor conditions at the facilities persisted, even after Congress approved a $4.6 billion border aid package in June. The money allowed the Border Patrol to quickly move children from facilities at the border and into better equipped shelters.

“One detainee alleged that a Border Patrol agent told a child who had spilled soup that the child would not receive more food unless the child drank the spilled soup off the floor,” Mr. Cummings said in the letter. “Detainees at Border Patrol facilities also told committee staff that they were pressured into signing documents in English without translation and denied access to telephones.”