Depends on the swimming ability of the child and the depth of the pool etc. Accidents happen around a swimming pool not through actual drowning but cocky horseplay that can mean a child falls too close to the edge, hits their head and can become unconcious. If it was my home pool and my kids had friends over, then I'd still be keeping an eye on them whatever their age. Same for the beach as well - I consider myself a fairly strong swimmer, but I've been caught in the rip a number of times and it is tricky getting out of it when that happens. I'm probably being over cautious, but perhaps that is better than underestimating the dangers of the water.