When my oldest was young he was naked all most all of the time
We have beaches here, but he was naked at the beach until he was about 3. Since we are a tourist location, and people from all over the world visit, it was pretty easy to spot the people who didn't think this was ok. My mom was mortified that I never had a bathing suit on him.
I'm not sure if I would feel differently with little girls. I think I would cover them about the same age in public...3. But at home, without prying eyes, I think I would let them go without suits until they were entering puberty. Then I think I would encourage them to wear a suit. Not that puberty is shameful in any way, but I think they would want to anyhow.