Well, if you have them living with the parents, then you feed the parents and they should do the rest. However, hand feeding is suggested due to the fact that it socializes them to being with humans and connects being held with food. If you are going to hand feed the babies then use an eye dropper and feed them a mush of bread (wheat, whole grain preferably) and milk (not skim, a little fat is good). If the babies are not "chicks" but just very young you feed them seed and millet just like you would an adult. If they are not eating seed by themselves then your only option is to handfeed, most birds typically do not feed themselves. Watch any nature program and the chicks are always fed by the mother by mouth.
What age are the babies? Some domesticated birds will not feed their young and you can buy a powder to mix with warm water to feed them at the local pet store. If the parents won't feed them and if they are still to young to eat bird seed then you will have to hand feed them or they will die.