These people aren't standing at the border asking permission, whitebread. They're unlawfully in the country which is against a series of laws passed by the u.s. congress like a bagillion years ago.
It's like you're hauling a few hundred pounds of weed down I70 to sell with your kid in the back, and you get caught by the cops. They arrest you and put you in jail but not your kid. You can't point to the kid and say it would be child torture if they arrested you, and get off. Otherwise all criminals would haul kids around with them like monopoly get out of jail free cards.