If a child is reported missing, an official alert goes out for a missing child, and police are dispatched to keep a look out, it shouldn't matter if it takes 10 minutes, or 10 days.

That's why most of the time there needs to be a deliberate amount of time between last seen and the report for a missing child goes out. More times than not when those missing kids are found quickly, it's because the alert went out and people and police were informed and were able to quickly locate them at a park or something.