I have twin baby girls of 1 year 9months old.One girl is not properly responding to us. She will not listen to our words.She is physically very active and eats sleeps properly but will not listen to us and she has not started talking.She will make her own noises never try to speak what I tell. She is not having any hearing problem. from past 2 months she is reacting when I call/shout at her. I am so worried sometimes on her behaviour. Some of my family friends said all kids will not grow equally some kids will take 4-5 yrs to listen/speak/respond.Is this commonly found in few kids?