lazy farmerette here, who can never find her tools, and am chronically broke (kids, need i say more). so i wanted the eziest, most natural method of chickie-introduction. i let a broody set in sept--but was still obsessively worried when a chick hatched in (cool) late sept, but decided to trust mama and you guys (mama only allowed one hatchling).
sooo--my experience: closed off the solid sleeping house and left the rest of the flock in the fenced area with roosts. they were squacky-mad, but got over it by the first night. i put my food dehydrator in it for baby warmth. it was in the 50's. i homemade some starter mix from a recipe in 'backyard chickens' and made sure their water was fresh. they really made mess of the water--so this was challenging. the awesome part was how the baby burrowed into the mom's feather--i couldn't even see her!!! mama kept her warm! then about 23 days old, mama and baby decided to escape. there are cats and pets everywhere-but they were still alive at the end of the day. after the 2nd day, mom had proven she knew what she was doing so i opened the barrier between the coop and laying house. i was a little obsessive--but the 3 roosters and 15 hens had no problems--i mean after the initial squawking! i kept an occasional eye out and fed the rest of the flock a LOT so they didn't get any ideas. i threw branches and firewood around the perimeter of the big yard that they go into during the day, and the sleeper coop, so there were plenty of hidey places. i learned that from youz guyz--and that is good info!
now, all is well, and mama has taken care of baby #1--so come spring, she will be a pro. i feel like a chicken farmer!
With my last hatch, i let mum and her chicks out with the rest of the flock on day 2. They are now 4 weeks old and they are doing just fine. Managing chicks is a lot easier when they have been set by a hen.