In all honesty I think she could be 2 1/2 or 3. My grandson is about that size and my daughter had hair that long at that age--she just looks quite immature to me but with lots of hair.
Oops there's jr next to her--i'm guessing she's 3 and he's 2 maybe????
Wish we could see more of Jr. in that picture. That might give us a better idea as to how old she is and IIRC she is about 18 months older than he is..JMO