Caring for a Baby Finch?

My father in law has two society, two zebra, and two Asian spice finches that laid eggs (not sure exactly which). 3 eggs hatched, but one of the chicks seems underdeveloped and has solely white feathers that don't cover his (or her) whole body. Could he or she have hatched later than the others, or could there be something wrong? The adults are feeding him or her, and he seems to be flying from one side of the cage to the other in short bursts, but I am concerned about him and whether there is something we should be doing for him. He has had finches before, but never had anything like this happen. I can upload a picture tomorrow when he is out of the nest again.