More than 4,000 unaccompanied migrant children are in Border Patrol custody, CNN has learned, marking yet another increase in the number of children held up in border facilities until officials can accommodate them in shelters that are suited for them.More than 4,000 unaccompanied migrant children are in Border Patrol custody, CNN has learned, marking yet another increase in the number of children held up in border facilities until officials can accommodate them in shelters that are suited for them.