Your little guy being last hatched is a week behind the first. If you want to see what a difference a week makes check out my post under Cockatiel pictures. "Todays' Baby Update" It shows two clutches. One is a week behind the others. The first one in the second clutch hatched 1 day after the last one in the first clutch. I would have to wonder if your small guy is warm enough to digest food properly. A heating pad on low with a towel over it under thier cage would probably help the little guy.