I don't know what to say about quarantine if that is an issue when they are so young, or maybe you hatched them yourself or got them from the same place? As far as the age difference, I have one bantam in with the rest of my standard sized chicks and they all get along fine. The standard sized chicks though are all breeds that I *think* are supposed to be pretty non-aggressive, so I don't know if that has made a difference. My biggest and oldest chicks are about three, maybe four weeks older than the youngest chicks, which includes the bantam. I watched them very closely when I first put the youngest in to make sure there was no bullying, and I set it up so some food and water was right in front of the Ecoglow (heater) at first so that the newbies didn't have to venture out too far to get food and water and could run back under the Ecoglow if they felt threatened. It seemed to work great! If you don't have a heater like that, you could do the same thing with some kind of box or make a little thing out of wood blocks so the tiny chicks had a place to get away from the bigger ones if they needed to.
