We put 2 3 day olds with 8 14-day olds, but it was arranged so that the little ones could get away from the big ones if they needed to. The older ones were in a huge watermelon box. I put a wire dog crate inside the watermelon box with the intent that the 2 sets of chicks could get used to each other by seeing and hearing each other. I didn't realize the little ones could squeeze through the wires, and in the morning, they were snuggling with their older "sisters" out in the watermelon box. The older ones didn't seem to bother them, but I kept extra food and water in the dog crate anyway so the little ones could "escape" back into the crate and eat in peace and get away from the older ones if they felt they needed it. Most of the time they hung out with the big girls, but I felt better about having a place they could go, especially for the first week. After that, they got too big to squeeze back through the wires, so I just took the wire crate out and they've been fine ever since.