You only need to supply grit when you are feeding the chicks other foods or treats. A chicken's food goes, as is, into the crop, where it is slowly funneled into a very small " stomach" for some digestive additives--then to the Gizzard, where it is 'chewed', that is, ground into material that can be digested as it moves into the intestines and so on... The Gizzard is best able to break down whole grains and other chunky bits that they eat when full of grit. Longest lasting grit is Granite. All other rock and stone is much softer, that it wears down fast and that is why granite grit is best choice and works really well for best utilization of feeds. My baby chicks are given free choice and they choose it with pleasure, Chick grit is fine Granite, as soon as they are given anything besides Starter Crumbles. Their tiny gizzards are at optimum function at an early age.
Yep, no grit is needed for starter feed. If you put some dirt containing sand in the coop for them to dust bath in they will
pick up their own grit from that.