Growing up, I had a friend who lived in a 2 bedroom house with her grandmother, her mother, her older brother, and her younger sister.
Mom and grandma shared a room. The 3 kids shared a room. Both rooms were small. They had barely managed to squeeze 2 sets of bunk beds into the kids rooms.
After everyone grew up and moved out, it was learned that the older brother molested and raped his youngest sister from about 10 yrs old until he moved out. The middle sister heard everything, but said nothing, as she assumed it was consensual, and blamed little sis for it.
Pretty messed up. I would not put children of the opposite sex in the same room past about age 3. It's just an invitation for something bad to happen.
Edit: Thumbs down all you want. Let me tell you, "Show me yours, and I'll show you mine" starts earlier than you think. And what sometimes follows isn't all that pretty. I used to teach preschool, we had a playhouse in the playground, someone always had to stand guard over it, as the 3-5 yr olds would go inside, and show and touch each others privates if not watched.