My 7 year old daughter always taking my 3month old babys nappy of?

i love her enough to let her mind my little jayden, hes 3months and everytime i walk into the room shes playing doctors with him... ino shes young so i dont shout at her. but when shes lifting his legs up with no nappy on? i dont no what to do... its been about 4 times now, and when i sleep in she comes into my room and gets jayden, when i walk into her room shes always touching his privert parts? is she curious? please help me, im a single mum with a teenager aswel, my lifes a handfull!