(CNN) -- Lawyers from the National Center for Youth Law say children haven't been able to shower or call their parents.
The team interviewed a dozen children in the government-run tent facility last week.
But the center's director said the children were terrified, crying, and worried about not being able to talk with the family.
Some said they hadn't seen daylight in days.
The allegations come as concerns mount over the growing number of children in customs and border protection custody.
A CBP spokesman said border patrol officials quote, "do everything they can to take care of unaccompanied children in their care."
However, a Homeland Security official said last week that the facility in Donna was 'significantly over-crowded.'
On Saturday, the Secretary of the Department of Homeland Security announced he is directing FEMA to join HHS in helping the border patrol.
Secretary Alejandro Mayorkas believes the combined federal agencies can help provide emergency shelter for unaccompanied minors crossing the U.S.-Mexico border.
The announcement comes in response to the surge in unaccompanied children which has overwhelmed border facilities.