>"So: if a state or locality has decided or later decides to specifically make a law specifically against "unattended kids going to school," that law would take precedence over this act. "States rights" are still in effect here."
Your posting is informative but doesn't refute that it is still not the Federal government's power to pass such laws (based on the Constitution). The States should make the necessary laws regarding such things and the State courts will interpret them and the State Executive branch will enforce them. If there is no State law about it, then that power is left TO THE PEOPLE.
Their passing such a law specifically DOES erode the States' rights to govern their people in a matter not granted the Fed by the Constitution. If the State wanted legislation in that area, it would do so, or is free to do so. In this case, the Federal law might step out of the way if there is a State law about it, but it is still overstepping, it is just doing it in a round-around way... they are setting a default law about something. Quite clever, actually.