If we are talking Tilapia, they are carnivorous and will eat each other until their body size gets too big to fit into their mouths and then they suddenly become vegetarians and will only pick fights from time to time to establish the pecking order. With that said, the little ones should be able to eat the same food as all the others in the same tank, preferably pellets.

As for adding the little ones in with the bigger ones, if it causes over crowding, then you will have a problem with the bigger ones constantly chasing the little ones especially if there is a breeding pair looking to spawn.

Mainly, it all boils down to space. To little, big problem....lots of room....no problem. You be the judge if what your are thinking of doing is going to overcrowd the tank and don't forget that it may not be overcrowded at first, but the little ones will grow and that will add to the overcrowding problem.

Hope that helps.