What is grit? And why do my chickens need it?
Chickens (like many birds) seek out and swallow small stones. The stones stay in the gizzard and help the bird grind and digest its food, much like a human chewing.
Chicks will not need grit until you start giving them treats or they go outside.
Chickens will naturally pick up stones and swallow them, but you should provide some free choice grit just in case weather conditions (snow/ ice) prevent them from finding stones.