Too many children drown, full stop. 1 is too many in my opinion.
I would suggest that nobody assume details at all about how or why this happened. The full story is never complete, and the facts change from one person to the next.
I only hope that if the public swimming pool is found to be at fault, they change their rules and regs to ensure this doesn't happen again. Unfortunately, it often takes a life to do that, which is the saddest part of all.
RIP little man.