My niece is 18 months old and she's seems to be very slow with her development. I have 2 other nieces and 2 nephews (1 of which is 7 mnths and is more advanced) and she won't interact with any of them. She seems like she is in a world of her own most of the time, she never looks anyone in the eye and never responds when i call her name. She doesn't talk either and most of the time she makes noises to her self. Sometimes when she sits on the floor she shakes her head side to side rapidly and this really concerns me too. Her weight is also a major concern, she only weighs 13lbs 15oz, but apparently the doctors are fine with this! Am i just being an over anxious auntie?!