What is the reason that you think you might need a child locator? Are you sharing custody of the child with an untrustworthy ex?
I cannot think of a reason why a child under 10 would be wearing a child locating device, except in the case that you are somehow legally obligated to send the child off with an adult you don't trust. We don't usually have children under 10 in sole charge of their own whereabouts anymore.
If you do have a child that age who is responsible enough to go to school on their own without an adult, they're probably also responsible enough to carry a cell phone to call you if there's a problem. The cell phone has a GPS. In the old days, of course, we just carried a quarter to call from a pay phone. The school would let you know right away if there were a problem. Are you worried someone will abduct your child under 10 but you don't want the child to know that you are worried and have put a tracker on them?