I have almost 6weekers and 3 weekers.  I have for the past 3 weeks had them next to each other in seperate brooders but they are in wire dog kennels wrapped in hardware cloth so they can't get to the younger ones.  I did try a couple of times to take an older one out to see the babies right out infront of their brooders but it just got too violent immediately.  So with some thought I decided to put them out together for a little outside time in a play yard with some crumbles on the ground to peck at.  Since the older ones didn't have any territorialy claims to the area all went REALLY well. They barely even noticed the younger ones.  They were all walking amoung each other just being chickens.  It was really nice to see since I was so worried.  We will probably be putting the older ones in the coop this wednesday and I was going to put the babies in a cage in their, but now I think I'm going to just put all of them in there together since it will b new to all of them and they can explore at the same time.  It might make it more peaceful.  I'll keep an eye on them, but I think it might be what works best for me.  Good luck to you