When I am teaching "adults" to scuba dive, I never turn my back to the students when they are on scuba let alone leave children alone in a pool with scuba equipment available for them to use in the pool and walk away from them to where I can't watch them. I would NEVER leave my students alone in the water even if I had to go to the restroom during class, I'd get them out of the water away from the pool's edge first (If I can't hold it until end of the lesson). This is nuts.