The key to integrating chicks at that age is to have lots of space so the little ones can get away. The more chicks the better, makes it harder for the hens to fixate on one chick. I currently have 11 9 week old chicks fully integrated with 11 hens and a rooster.
I started with locking them in my broody area of my coop for about 10 days so they could interact with the flock but not get hurt. Then I wedged the door so the babies could come in and out, but the hens cannot get in. They only used this for a few days, and when I noticed it wasn't being used, I removed the door. After about a week of staying in the coop all day, they are now venturing out into the run. (coop is 8X12 and the run is 30 ft X 50 ft) They still get chased if they get too close to a couple of hens, but most of them ignore them. My rooster is very protective of them and comes running if he hears them cheeping.