Hiya, and welcome to BYC!
I concur with the other greeters, tomatoes are fine, the leaves are not.
For baby chicks...like said above, they should only get their chick crumbles until at least a month old, and then if you give them something else, very small quantities first, and provide grit.
A "treat" they can have is wetting their mash. I use a couple of plastic peanut butter lids to put some crumbles in, spray water to soak them, sit them in the brooder, and watch the chicks go wild!
Scrambled eggs are one of the safest first treats that most chicks tolerate well. We start them out with a very small amount the first time, after they're about a month old. We wait until they're about 6 weeks old to start anything stronger like fruit and veggies. Always make sure they have grit though if giving them anything other than their feed.