It sounds as though your daughter is imitating her younger brother, either consciously or unconsciously. She has somehow gotten the idea that being babyish is the thing to do. Are you sure her little brother doesn’t get more than his share of praise and approval? And are you finding opportunities to praise her for being older and bigger? “I’m glad you’re such a big girl and so able to do things for yourself.” Tie privileges to age-appropriate behavior on her part. “Yes, you can go and play with Cindy today because you’ve been acting like a big girl lately. She wouldn’t want to play with you if you acted like a baby.”
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.