Newborn Baby with Under-Developed Lungs?

I can't help with the underdeveloped lungs, the hospital should have given you advice on that. But there is not reason he cannot go into the binet for as long as needed. If your daughter is still doing good in a crib keep the baby in the binet for as long as needed or possible. Your daughter is probably wary of the baby because she knows that he is different, realizes that this one is not just visiting!