Oskar seen rear nude in a changing room at the beach. Then he stands up against a teenage girl. It is implied that he is kissing her genital area, or possibly performing oral sex on her.
Nikolai (Evgeniy Kraynov, 13) and Anatoli (Artur Smolyaninov, 15) catch fish in a river, both seen nude from distance. Brief rear nudity of Anatoli after swimming when he is changing.