I have had good luck with chicks of different ages, put 1 week olds in with chicks of different ages, up to 8 weeks old. Everyone was fine. But they had a nice large area. Smaller ones stayed closer to the heat lamp, older ones stayed further away. I had 2 feeders and waters and had them on different ends, now they mingle and I have even seen one of my little ones sleeping on the back of a bigger one. Of course by the time I got my camera it was not up there anymore!