I usually give the new kids a small space where they can see and be seen if I have any questions about the behavior of the chicks already in the brooder. Given some time to look at one another things usually resolve fairly quickly.
Tolerance of new ones is both an individual and sometimes a breed tendency thing. I was surprised that the Delawares (2 weeks older) accepted some baby BAmutts with little or no problems except for using them (like everything and everyone else in the brooder) as trampolines.
My sizzles took all of about four minutes to accept some new baby dels this week, took the BAmutts a bit longer though they were MUCH closer in age - six days apart.
Watch, don't assume. When in doubt, give them time to watch one another. I keep the Sizzles in the house brooder despite their age because they actually ARE good with the new babies that I've been getting in every week or ten days. I move the others that are more active or less accepting out to the big brooder as needed.
Good luck, keep your eyes open. Usually it goes pretty well.