I have a 10 year old daughter and she is doing the same thing with her 8 year old brother I have to supervise them when they play together but still give her her space. It is very common in Downs girls from what I have studied I have talked to the doctor as well and they tend to be very sexual just watch them.
PJ is correct about the sexuality aspect of a downs child. especially a female.. their spatial awareness and ability to understand the boundaries between family and non family members to express themselves upon is greatly diminished.. it’s a very sticky situation to say the least.. I replied to another question regarding something similar earlier today.. as I said to them, “ the biggest thing to worry about is (sexual fixation) if it aloud to manifest it will be a future major problem as some downs don’t recognize the difference “sexually” as PJ says keep an eye on it... once a sexual fixation starts to manifest, it is hard to break..