Chicks are fun aren't they. Eggs cooked in any form seem to be the big favorite, bugs like mealworms/ crickets are a hit, leafy greens, yogurt, soft fruit like banana, papaya, strawberry, tomatoe, mine like some of those whole grain cereals you cook. You can really feed chicks about anything you feed adult chickens (think about what chicks with a broody do, they eat anything she eats and scratch in the dirt from a few days old), just in moderation so you don't unbalance their diet (usually around 10% treats) and be sure to offer them grit if you feed them other treats. A lot of people also start putting clumps of dirt/grass in the brooder pretty early for entertainment and to start getting them exposed to local coccidia so they can start building up their immunity. Long thread with a lot of suggestions.
https://www.backyardchickens.com/t/181429/good-treats-for-baby-chicks
