Don't feed them anything but their real food. If you feel the need then moisten it & give that to them as a "treat". They need all the proper nutrients to grow and anything other than their food dilutes those nutrients.
I am a proud treat giver: tuna fish, watermelon, yogurt, strawberries, scrambled eggs, trout, cucumbers, alfalfa, peaches, raspberries, captain crunch with the berries.
Momma hens let babies have treats. Momma always knows best.
You can feed them treats as long as they have access to chick grit and as long as the treats do not make up more than 10% of their diet. Mine love strawberries.