Hi, can we get pics of your new sweeties. How old are your older rats? Older rats might be annoyed with super young rats but they usually settle down after a while. How many babies did you adopt? That's really good that they will have each other to play hard with and then learn to respect the older ones.
Most babies leave their mom at 4 weeks. Some breeders wait until 6 weeks. That is considered young and could be dangerous to start intros. Do you have them all living together already? Or at they just being introduced slowly?