Nudity is shown in a handful of scenes.
Naked (barely pubescent) children, naked adults. Full frontal, but not lingeringly sexual.
Also, sexual activity between various adults. Free love is a major plot point of the film, as is the fact that the protagonist, a 10-year-old girl, grows up in this environment. She sees the sexuality of adults around her, including activity between her parents and other people, sometimes simultaneously.
Three children go around in underpants quite a lot. There is a scene where they are on holiday and the kids climb to the top of a diving platform. They are naked, but seen from a distance. At the top, they are seen close-up but from the waist up. While swimming, a boy's and a girl's genitals are seen fleetingly. Shortly afterwards, while skinny dipping with adults, all that is seen is the occasional butt.
There is one female and one male adult full frontal and one scene with a woman in a see-through red dress. Apart from that the nudity consists of an occasional pair of buttocks and some breasts.