You have a mixed question there. Chicks can remain on starter until they are about 18 weeks old and then gradually switched to layer feed so that they are on layer by the time they start laying. You can also switch them now to a grower feed if it is available in your area until they are about 18 weeks and then switch to layer. If you are wanting to integrate your chicks into the main flock at this time then that is a different story. If they have been only seperated by wire and they get along through the fence, then you can integrate them at any point. They will eat the layer feed or whatever you have the older ones on. If you allow your younger ones to go back to their area at night then you can feed them chick feed at night and in the morning just to keep that in their system until they get a bit older.