A fertilised egg takes 18 days to hatch. When hatched the chicks should be pink and healthy, and squeak to be fed. Feeding is carried out almost exclusively by the hen by regurgitating a substance from her crop, known as crop milk. There are two points worth noting on the feeding of chicks by the hen, the first being that baby budgerigars are fed on their backs which is most unusual for birds and secondly the hen can grade the feed she is giving to the chicks depending on their ages, so that the older the chick the more seed content of the crop milk.
Do not handle chicks when you have unusual smells on your hands. A fancier once told me of an occasion when he picked some tomatoes from his greenhouse before going down to his aviary. He inspected his nest boxes and chicks, the next morning, to his horror, ten of his eleven chicks were dead.