Please i need help on what to do with my daughter...?

O.k well im a single mother of two...My son is 7 yrs old and my daughter will be two next month..Well her daddy isn't really in the picture only when he feels like being a dad for them he comes around..Anyways lastnight my daughter was in her room playing with her toys and i was cleaning ...Well when i walked by her room i saw he kissing her doll...I thought it was cute at first but when i kept walking by i saw her pretty much makingout with it( mouth open and all)...I couldn't belive she was doing that shes only going to be 2 yrs old and i don't find it very normal..I don't have a boyfriend and i never bring guys to my house ever...So i'm wondering where could she have seen that...Then while i was watching her she started to lift up her shirt and rubing her tummy ...I didn't know what to do...So i called her into my room and took the doll away... I really need help is this normal for a two year old to do this??? What should i do if there's a next time ??? I'm really freaking out