I put my pullets, that are 8 wks old, in with my year old hens about 3 weeks ago. I have 6 of each and a variety. My 6 adults didn't seem bossy with one another at all, always getting along. I used to comment that I didn't have anyone at the "top of the pack". Well, when I slowly introduced our 6 newbies to the others there emerged a "pecking order". One of my Buff Orpingtons became very "Pecky" with the babies. It also seemed one of my Barred Rocks was 2nd in line..also trying to peck or chasing them but not as aggressive as the BO. I started by bringing the babies out for short periods into the run every day and staying right in there with them. I still brought them in at night to sleep in house. I also free ranged all of them in the yard, which was totally fine. Then, on the weekend I began leaving them in for longer periods of time and watching them a lot. I hated the pecking and chasing but it didn't seem there was any blood being drawn. The biggest issue was the babies not being able to get to the food and water. The 2 bossy ones would stand guard and keep them away. I ended up putting in an extra feeder and waterer and then I rigged up some bins and walls to give the littles a place to run and hide and also to go under if it was raining and the bosses wouldn't let them into the coop. This worked great. They were able to get to food and water and would either run under the coop or under the bins or walls I created in the run. At night the older hens would go in first and then the first couple of nights I had to put the babies in and encourage them onto the roost (of which I have 2 different ones). After that they'd go in on their own. The funny thing was that, even though the bossy ones wouldn't let the babies around them in the day, at night the little ones would sleep right near the bosses and it was ok. I thought that was so weird. Anyway, it's been a few weeks now and they are doing so much better. The little ones still get chased a bit but they are big enough to get away. I'm going to keep the extra waterer and feeder in there as well as their hiding spots until the babies are more full grown. All and all it has gone very well and a lot better than I expected. I really think space, patience, and the extra food and waterers can't be overestimated. The other thing I had read on here from someone else, that I tried, was to distract the older hens when adding in the babies. I would do things like take a shovel and dig up some dirt in the run to give the older hens something to do instead of focusing on the babies being in there. These types of things helped as well. Good luck.