If possible wait until they are closer in size to the older hens, then put them in a pen inside the coop or run for a week or two so the other birds get used to them, then you can introduce them while free ranging, and eventually put them all in together. I had some very bad luck introducing new birds. I had three 10 month old Barred rocks, and I tried to add two EEs, one who was the same age- got along fine, and another who was only 7 months- at first things were fine, then three weeks into it the BR girls scalped the 7 month old down to her skull, she lived, but it was awful. So just be cautious, some folks have no trouble, but many times older birds can be territorial and quite mean to new ones, especially if they are younger and smaller. Good luck!