"Chick grit" is what you want. Its smaller than "poultry grit" but the same stuff (usually crushed granite), just different size. Large grained sand works good too. I simply mix a table spoon or two of grit in with the chick starter feed (not sure how many chicks you have) but they will eat what they need an ignore what they don't want to eat, so you don't need to put it in a separate feeder.
As far as dirt goes, I have always put a small box of dirt and sand in the brooder after the chicks are one week old. This can help build their immune systems and I firmly believe in this over using medicated feed. Chickens have been around a lot longer than medicated feed has, and in the wild they aren't born in sterile boxes and pine shavings, they are born and raised on dirt and grass. Yes there is a risk of coccidiosis, but exposing them early in small amount is better than a sterile environment and then at 6 weeks putting them on dirt with no immunity.
Hope you sick chick pulls through okay.