Children have traditionally been thought to be under the exclusive authority of the parents. In the last century the “best interest of the child” argument has become a factor. I googled that to see what is the constitutional basis for courts to get involved and override one or both parents. While not a very thorough search on my part, it seems to be derived from judicial rulings that are largely done in the last thirty years. Of course in family court, best interest goes back further when men get their parental rights taken away so the mother can exert near total control.
Give courts enough time and they become the law, not interpreters of it.
Right. But a parent still faces criminal prosecution for leaving a child to die in a hot car. Parents have authority over children and are responsible for making decisions for them, but children are human beings who are supposed to be protected under the law.
The intricacies of that term "protected under the law" have a lot of gray areas -- and a whole bunch of slippery slopes in either direction -- for sure.