All chicks love finely chopped hard boiled egg. Spaghetti noodles are also a trip (they chase each other around to grab the noodles out of each others mouths). Mine also love cooked oatmeal. Some feed their chicks chopped grapes and the like or yogurt.
Without grit keep the treats soft and mushy and make sure treats are a small part of their diet with starter being the majority.
When they are a few weeks old mealworms are a HUGE favorite but be sure to introduce grit if they eat mealworms or grass.