My chicks (Wyandottes) are just 3 weeks old and eating all kinds of stuff with no signs of trouble. They've been in their coop now for almost a week and they forage in their yard and get treats twice a day, a medicated feed, plus a little scratch to keep them occupied when they're in the coop at night. I suggest that you try a single item (we started with lettuce torn up really small for those tiny beaks) and see how they do. We started that when they were still in their brooder and we've since given up watching TV. Watching chickens eat lettuce is way more entertaining!
I was surprised that they didn't like strawberries when we offered them, but I think the flavor is too intense for the littler chicks. Just like humans, they need time to develop their palates. Now I pick the stunted berries off our plants and toss them into the chicken yard and they all race to get them. They don't like broccoli yet, but I can totally understand that
. We give them fresh spinach, apples cut into tiny chunks, plain yogurt, tomatoes, and thawed frozen peas. I have a box of Cheerios that is a little stale, so I think I'll try those tomorrow.
I think you can go ahead and start trying them on different treats anytime after they're eating grit. Oh, and if you get the chance to catch a moth, drop that in with them and watch the fun. It was like a chicken Super Bowl.
Enjoy!
Corly