House of Fun

So Jeanne's friend Olga from Russia told her of this three year old kid up there. His parents came to pick him up but he did not want to go with them. He kept running away and putting up a fuss. The parents are good parents and they weren't expecting like abuse or anything of the sort. Eventually, the mother told her that, like everyone who lives in Kazan, they live in a two room apartment. The kid was asleep and they were having sex in the other room but were really loud. During the most appropriate time, the kid walked in the room and from what a three year old kid could make of the situation, he thought his father was attacking his mother. So the kid is now extremely scared of his father. How do you explain to a three year old about sex?