Are you familiar with human babies? Anything a baby with no teeth can eat, your chicks can eat without grit. Think soft, mashable, easily dissolvable. So that includes watermelon (no seeds), strawberries, cheerios, bread, cottage cheese, banana, stuff like that. Serve it in large pieces so they have to take bites with their beaks - rather than dicing it and letting the chicks try to gulp pieces whole.
The purpose of grit is the same purpose as human teeth. It works in the crop to grind up food so it can be digested. So if it doesn't need ground up AT ALL, then it's fine. (Chick feed dissolves, so doesn't require grit.)