I have two bantam cochins that have been running with a large group of standard chickens. They really need to go with the smaller chickens as they are just too much smaller than the big ones and are on the receiving end of some enthusiastic pecking order stuff. I am wondering if I should wait a couple more weeks for the tinies to catch up a little in size and then combine them all. I have 9 babies and two bigger 5 week olds. What do you think?
2 bantams and (9) week-olds? That actually might work. Watch them for a while and see if there's any problem. Bantams are easier, in my opinion, to integrate with younger chicks. Or you can put them in one brooder, separated by chicken wire for a few days, then take the wire away. I think you'll do fine.
I put a brood hen and 7 chicks in with my older chicks, about 4 weeks at that time. Brood hen keeps the older chicks away, but when she's not looking the little guys will try to bump chests with the old ones, one quick peck and the little guys don't want to play. I would make sure I've got a low square of plywood 12"x12" that the older birds can't get under, so the youngsters can get away from the older ones.