I am new to chickens this year and have ages spread out over 3 1/2 weeks and I have just kept the babies by themselves for the first 4-7 days then introduced them to the older ones and it seems to have worked out. It seems to stir up the pecking order a little, but not that much. the older ones just make sure they are on top. Hope it works out for you.
As long as they are confortable in the brooder and they have enough space and feed they'll be fine.
But to try to prevent any pecking you might wanna put a red brooder light this will distractem from peckingf at younger chicks
How does the red light help with stopping pecking? Just curious as I will be adding in a couple chicks that will be a week or two different in age from my current chicks and I want to make it as easy for them as I can