For the first few weeks I would only give them chicken starter feed or cooled scrambled eggs. Keep treats for later on when they're a bit older. Check out Chickenlandia on YouTube. Dahlia has a book about chicken raising and she's really knowledgeable. Did you get sexed chickens? If not, then you need to prepare yourself and have a plan if you have too many cockerells (young roosters). I just had to rehome my Golden-laced Polish because it was extremely obvious he was a rooster (gorgeous guy) and I don't keep roosters in my flock. Many suburban neighborhoods do not allow roosters, so google your town laws on chicken-keeping. You don't need a rooster to get eggs and my girls are my pets.
Also, baby chicks on chick starter feed don't need grit. I don't know the temperatures where you are and the chicks need the warmth of the heater for the first month, so I probably wouldn't take them outside yet. That being said, I also wouldn't brood them in the house because the dust is awful and quite difficult to clean up. I brood mine for the first month in the garage and then move them to the coop. Since I'm integrating them into an older flock, I have them in the cage with the door open but blocking easy access by the older hens. The babies dug a tunnel and run around the coop during the day. They aren't quite big enough to get out and go down the ramp. You could put a lightweight cat toy on a string and dangle it. Just make sure you don't leave it behind so they don't try to eat the string,
