When the gang decide to cross a river, the boys split in two groups. Those who can’t swim use a small boat, and those who can, strip naked and put their clothes in the boat. Most of the boys have rear nudity but there is also some brief frontal.
While the boy (12) is skinny-dipping with several of his friends, his sister throws their clothes into the water because they won't let her join them. Mostly rear, but some frontal nudity.