This used to be called "playing doctor". Sounds like they needed more supervision at Grandma's house.
What did this look like, exactly, do you know?
Both were nude and the girl was laying with her legs spread. The boy was kneeling between them
Jazzygirl993: Don't know why either one was nude -- you have to ask Grandma that. 7 year old is old enough to warrant "privacy" when changing/ taking baths and so forth. 4 year old is almost at that point too. Don't overreact but teach each one -- especially the 7 year old to have set boundaries on who touches/ looks at their private areas. Also have a separate conversation geared for the 4 year old's level of understanding. Teach them that NO ONE has a right to touch / look/ feel your private area OR even get into your private boundaries -- which is basically about 1 foot around the outside of your body WITHOUT your permission. Mommy and Daddy have to help take care of you and so do doctors/nurses but even still -- it needs to be ONLY when you are sick or have a boo boo. Kids are curious -- they see ALOT on TV and COMPUTERS and so forth. They HEAR folks talking and they want to see it for themselves. It is up to you to help guide them in a calm and matter of fact way -- the BOUNDARIES of their personal space and their person. They are to also respect that same level of boundaries for OTHERS! Hugs, because I know as a Mom -- this is stressful and it doesn't help that they did it at Grandma's house/ with nephew seeing. It starts all types of dumb words -- when in reality, you can help nip it in the bud and let it go. Show them by not letting them in the room when you change clothes or go to bathroom so they can understand PRIVACY!