Are fat babies unhealthy??

Hey all. I was just wondering if "pudgy" baby budgies is unhealthy, or has any bad effects on the babies? They are all active and alert, VERY vocal....but they are a little chubby. Then the other day I was, as usual putting the babies back in their nest box for the night (they are constantly climbing out of their nest box!) When I picked up one of the babies, the oldest....it was like he was sort of stiff, he held his feet out and started shaking. It wasn't cold, but I held him for a bit and warmed him up until he became back to a "normal" state then I put him back for the night. I was concerned, but after that I didn't see it happen anymore, then today I checked and I found him dead. :cry:
I don't know why this happened, was he sick? Did he have a disease? Are the others in danger of the same thing happening??

And an update on the newly hatched baby....I was unable to get ahold of the breeder I know. So I just waited it out like Mike said to do, and sure enough the parents finally started to feed it! Since then I've had a second egg hatch...she hasn't fed that one yet, but I think she waits until the yolk is completely absorbed. The I have one more egg to hatch....so I think she's gonna do alright.
-Mandi
PS, mike thanks for the handfeeding sites!