I had to stop watching this film
About 30 minutes give or take I could not watch this any longer b/c the scenes with the children felt like porn.
I thought it was exploitative. Normal kids do not act that way, IMO
This probably reflects a cultural difference, or the difference between European & American film.
As other responses on this thread point out, it's actually very common for kids to hang out together in their underwear, swim trunks or going swimming nude together.
Unless something sexual is going on, it's usually pretty innocent. But kids are going to be curious about bodies as they get older anyway, playing doctor, house, etc.
So films like this are being realistic in portraying it.