If you've got kids (or you yourself) who aren't strong swimmers consider 'drown-proofing'. I've taught a number of kids, takes maybe a half hour.
It works like this. Start with your head above water, body vertical. Take a breath. Let yourself sink, spreading arms and legs as you move downwards. Pause a beat. Push yourself upwards by pushing arms back towards your sides, legs together. Exhale as you do this. Once your face is out of the water, inhale. Then, like they say on shampoo bottles, repeat.
This won't do anything for rough surf or undertows, but it does mean that if your kid falls into someone's pool, they're less likely to panic and drown.
I'm a 'sinker' (negative buoyancy, can't float) and it works for me, so buoyancy is a non-issue (but know that if your kid is also a sinker, standard strokes like they teach at the Y pretty much don't work; I had to come up with some variants on my own - but they'll have better luck with a sidestroke than a crawl).