As far as i know the hamster fur grow in their 6 or 7 months old, but the male hamster fur grow much than the female. I think its b'coz of their nature and of course its in their gender and i also know that female became fatty one than the male. And about your next question you cannot play the babies of your hamster unless its eyes are open. Coz it is the sign that your hamster can live alone. Don't try to play with your baby hamster coz the output can be severe, the mother hamster can smell your sent in her baby and if these happened she will kill her babies or put them in her pouch.