First of all, that is not correct. In one of the cases one parent was also a US citizen.
Second, even if in all cases the parents were not citizens it does matter because the US citizen child's due process rights were not respected.
> They deported the parents and their kids along with them. Should they go into foster care instead?
There should be a hearing for the US citizen child to determine what to do with them. Even if both parents have to leave there may be other relatives in the US legally who would be happy to care for the child.
Second, even if in all cases the parents were not citizens it does matter because the US citizen child's due process rights were not respected.
> They deported the parents and their kids along with them. Should they go into foster care instead?
There should be a hearing for the US citizen child to determine what to do with them. Even if both parents have to leave there may be other relatives in the US legally who would be happy to care for the child.