I agree, baby chicks should have food at all times. Water too. You can also give them dried meal worms (good protein!) live worms, and grasses as treats. If they were with the Momma hen she would take them to the field to eat with her. With adult chickens I'd say if they act like they are hungry all the time (jumping up on you because they think you have something to eat, trying to grab the eggs you collected, etc), they are hungry!