9 yr old daughter’s curiosity

I have a 9 yo daughter and 7 yo son. They get along great, are basically best friends and sleep in the same room together. I believe my daughter is in the very early stages of puberty and is getting curious about things. We found out that when they are alone in the bedroom together before they go to sleep, she has gotten her brother to take his pants off so she could see and touch his private parts. My wife and I are concerned and not sure how to handle this. I’ve had a conversation with my daughter about boundaries and what is and isn’t appropriate behavior with her brother. We also have some books on the way. We are considering separating them to different rooms but that seems like punishment for what I think is normal curiosity. Has anyone had similar experiences? Advice? Thanks