I slipped and went under in a paddling pool in a park when I was 7. I must have got my feet back on the ground and pinged up within a few seconds, but it felt like I was drowning at the time. It must have given my granddad a huge shock.
I still stay close to my 9yo much of the time. He's working on his 25m and deep water swimming in lessons, but his treading water technique is not refined and it's hard to judge if he's struggling, and I wouldn't leave that to a lifeguard to notice if he was. If he's well within his depth I'll give him more range of space.
He had an incident at a public pool recently and hit his head while getting off a waterslide. We were well within pool guidelines, the 11 yo was at the bottom already, DH at the top, I was seperate and in an adjacent pool and heard crying a couple of metres away from me as DS approached the lifeguard and it seemed to take an eon to get myself through the pool to an accessible point to get to him (he was already accompanied by DS 11 and DH). I'm strong at moving through water too- can swim a mile in cold open water. It's not something you want to be doing in an urgent situation.
DS1 was a more refined swimmer at 9 having not lost lesson time due to Covid restrictions and that was the start of me using another part of the (lifeguarded, quiet pool). He told me to go and do some lengths and it only really occured to me then that he was sensible and skilled enough to leave within his depth and that there wasn't a rational argument not to.
Pools have strict policies on children, usually u8s and often even tighter on u5s for good reason. It's not just swimming ability, it's having enough maturity to have a bit of survival skill if there is an issue.
I'm not saying this as a pile on, but there are people reading this thread who think that lax and distant supervision of young, non-swimming children is acceptable and tbh, most people who would rather sit poolside than be in with their children are not experienced, aware swimmers and are not making a well-informed choice.