Would you let your 7 & 9 year old children scuba underwater, even in a shallow pool, unsupervised?
When I owned a pool, the kids were always under adult supervision, if not in the pool, on the deck watching. Kids to stupid stuff at times, it is how they learn.
If there were any scuba equipment involved, I would be in the water with them to closely monitor what was going on.......No way I'd leave them alone for 1 second.