Cinderella, Snow White and Sleeping Beauty were never dressed in an infant princess costume.  As babies they were wrapped tightly in blankets to protect them from the cold. Even a three-year-old child would know this; the storybooks have this in pictures for your information.  I hate to say this, but a mother who does not see this did not have a mother who read fairytales to her; likewise, she herself does not read fairytales to her child.  If you really do want to treat baby like a princess, dress her up the way infant princesses are dressed: wrapped in a blanket!