My 9 week old DD has not socially smiled yet. She was born 2.5 weeks early and not sure if this is relevant. She will track a brightly coloured toy, appears to look at faces and to have good eye contact. She also seems to show signs of enjoyment when we interact with her (kicking legs, excited facial expression). When does not smiling become a concern? Has anyone else had similar experience and what was the outcome for your baby?