That does seem pretty unambiguous to me: if they're holding the parents for immigration offences, by law they have to separate their kids from them because they cannot imprison the kids too. I think the US media is outright making people less accurately informed on this. The most I've seen is a brief mention that "US protocol prohibits detaining children with their parents because the children are not charged with a crime, while the parents are", without explaining what this means and the fact that this is a legal settlement that the US administration cannot modify.