I never give treats before about 4 weeks of age so they know without doubt the crumbles are their feed. When I give treats I give cooked rice, cooked egg and yogurt. I add crumbles to it. As long as they are getting commercial feed for the bigger portion of their diet they won't need grit.
However, they love to dust bath and scratch and peck. You can toss in a bit of play sand and crumbles so that they have something to peck and scratch around in to eat. You can also buy tiny grit for caged birds at the pet store that will work for chicks too.
This morning my chicks are getting their first scrambled eggs and yogurt!