A responsive smile is a smile a baby gives when a baby tries to respond to pleasant things or something that makes him feel good. Whatever creates a sense of happiness in your baby's heart, your baby will respond with a smile. The responsive smile of a baby at 6-8 weeks old is like a smile when he feels comfortable as you tackle him in the cradle, as you embrace his tiny body, as you put him to sleep with the singing of your voice. Pay attention to your baby's response when you do these things, your baby will surely reward you with an adorable smile.