AN> Another problem with the tiels is that every couple of months
  AN> (sometimes sooner), they lay eggs. When their babies hatch, the tiels
  AN> hiss loudly and bite their young and throw them out of the nestbox.
  AN> Sometimes after a couple of days/weeks they'll abandon all their eggs.
  AN> The same guy who said he had a green tiel, told me that tiels NEVER
  AN> feed their babies--he says he has about 80, they started off with a
  AN> pair and after hand-feeding the babies, his mother can't give them
  AN> away! I know this isn't 100% true, but could it be possible for the
  AN> cockatiels who are kept solely as pets and not for breeding purposes?
 
My gentle, friendly hen Belladonna fed her babies faithfully, at least in the 
first few weeks.  As time wore on, we noticed that her mate, the mistrusting 
Puck, did most of the feeding.
Puck is, as best as we can tell, the victim of bad nutrition as a young bird. 
 He was fed Purina Chicken Scratch, which is too high in protein for 'tiels.  
He's a high-strung bird.  A behaviorist would assume that he has been abused. 
 We've had him since he was about 8 weeks old, and we have never abused him, 
nor do we have children (or unsupervised visitors) who might have abused him. 
 He likes to bite. 
He has been a good father, though, and we will continue to take good care of 
him.
Your birds may be abusing the babies because they want to start another 
clutch.  Cockatiels have a very strong urge to reproduce!
As far as the egg laying goes, I've seen suggestions that you feed the 
cockatiels cucumber.  This is supposed to start a moult, which will stop them 
from laying eggs, but I've always wondered if the stress of moulting isn't 
almost as bad as laying eggs.
Another suggestion I've seen is to cut them down to winter light levels.  
--- MacWoof 1.5.3
---------------