YOGURT. Mine are insane for it. They are just over 3 weeks old. But they do get it everywhere! I just give them plain yogurt bc it's the kind I eat, plus some construction sand and it seems to do just fine.
I present small granite grit to my chicks at 3 weeks go easy on the treats unless its very high protein like boiled egg about 25 % the starter is fourmulated to medicate and give them the proper amount of what they need lots of protien .