To take a migrant child from her parents at a U.S. point of entry, place her in a just-erected government tent city, and keep her separated from family costs the federal government a whopping $775 per child per night, according to the Department of Health and Human Services — more than twice what it would cost to house the children in detention with their families, and nearly six times more than a brigadier general's or rear admiral's housing allowance for New York City.