Hens go broody when you don’t want them to… and won’t go broody when you do. 
My two youngsters (5 weeks) went out with the big girls (8months) last week. I made them a hidey hole by cutting a hole too small for the older girls in a cardboard box. Whenever the big girls start to pick on them they run into their box. I haven't had a single problem. This may not work for everyone but it has worked for me so far.
