A child is chosen to leave the classroom and wait just outside the door. Everyone changes places.
Another child is then pointed to, and they must then hide. The first child comes back into the room and must find who is missing. They may ask for clues if they get stuck.
This really needs a classroom that has somewhere you can hide a child. We have a small room between two classrooms where a child can hide. If you don’t have this, you could use a walk-in cupboard.