Here's the difference between mine when they were just born and the larger one is 2 weeks. I had to separate them.Got some new chickies this weekend! We got two australorp, two buff orpingtons, and two speckled sussex. I also have several in the incubator due to hatch this coming weekend. Question: these new ones will be maybe a week and a half younger than the ones I just got. Can I put them together or should I wait a few days?