WASHINGTON — At least 18 infants and toddlers younger than 2 years old were separated from their parents for at least 20 days because of the Trump administration’s “zero tolerance” policy at the southwestern border, according to a report released on Friday by a House committee.

Those findings were gleaned from records that the House Oversight and Reform Committee obtained under subpoena on at least 2,648 children who were separated from their families, the youngest being just 4 months old.

Some of the children were kept apart for as long as six months and 241 of the children were kept in Border Patrol custody longer than 72 hours, some as long as a week. Under federal regulations, migrant children must be transferred to shelters managed by the Department of Health and Human Services after three days in Border Patrol custody.

“My hope is that we can all agree on several basic points,” Representative Elijah E. Cummings of Maryland, the committee chairman, said on Friday. “Anyone in the custody of our government — especially a child — must be treated humanely and with respect.”