Because my fingers hit order on the hatching eggs pages faster than my brain thinks, I have had five staggered hatches so far and have 5 to go. We have had no problem integrating the older and younger chicks. This is how we do it:
I have a small cardboard box about 12x10 and I have two kennels together with the tops off with the openings facing each other.... one the extra large size and one the medium size. They have one of the cage doors seperating them, so the the two groups can see each other at all times. I have a brooder lamp over each crate. And the medium one still have a stuffed animal or two for comfort.
1. From the hatcher into the small cardboard box with pink stuffed bunny under lamp to finish fluffing and rest for 24 hours or so.
2. From the small box to small kennel for the next 48 -72 hours or so until I know they are eating and drinking and pooping. And this gives enough time for the older ones in big kennel to adjust to presence of younger ones.
3. Move the younger ones into the bigger kennel and WATCH VERY CAREFULLY for several hours to make sure everything goes smoothly and everyone integrates. As I bring younger ones over, if I know for sure I have any roos in the big kennel, they get taken out to the "boy pen". A seperate tupperware crate with lamp for the boys to hang out until they get their new homes.
Haven't had one single problem with integration yet, even when I put Peanut (the australorp with the cyst) in with the big welsummers. She has never even been pecked once and she is TINY!
Hope that helps.