@Braulio ********
no child passes immigration on their own. Kids “flying alone” are accompanied the entire way. They are the first/last to enter/exit the plane and do so with an appointed airline staff member who does everything with them from waiting outside the bathroom to security checks to immigration to baggage and stays with them during layovers or they are sent to a holding area and then taken to their gate for the next flight.
The only thing they actually do alone is FLY, and the air staff know who they are and take over in flight. Upon landing they are handed off to the next appointed airline ground staff who gets them safely to their next flight or through immigration, collecting bags to their waiting guardian.