are they with a hen? or under a light?
i fed chick crumbs for 4-6 weeks and then they went no to growers - their beaks need to be big enough to manage the bigger size. then onto layers at 12-14 weeks - or finishers if they are for the table.
what brand feed are you using? usually the feed store would hold info on what age the feed is for. big brands usually have an advice line too.