Children showing private parts on FaceTime to cousin

A while back my daughter (5) and niece (6) were FaceTiming each other (on tablets) while my sister and I were FaceTiming (on phones). We found out they were showing each other their butts. Then again today, they were FaceTiming and I told my daughter to FaceTime in the room because she was being too loud and I couldn’t hear my sister. I found out tonight they did it again even though they both have been talked to about this before. To me this is weird… but is it a normal little girl thing to want to see/show other people’s parts? My daughter has only known proper terms (vulva, vagina, etc) because kids that know the terms are less likely to be abused.