Finches Had a Baby?

I have 2 zebra finches, one girl and one boy. They have had a baby, I don't know the sex of the baby yet. The dad does all the work. The baby is now out of the nest and getting about really well, but now the dad chases round the cage and is being horrible. The baby is still asking to be fed. Dad feeds it sometimes, but not much. Why is the dad chasing the baby. The baby sits at the bottom all the time. I'm scared I'll wake up one morning to find that the baby has died. What shall I do?

By Tracy