I had a Brazilian Rainbow Boa go AWOL for three weeks. I found him in the snake room getting a drink from a water bowl I'd put on the floor.

If this is a young ball python then keeping a small live mouse in an escape-proof cage may lure him out. Ball pythons are most active from dusk to dawn, that's when they naturally hunt, so if you or your son sits quietly in the room you may hear the snake moving around at night.