and Welcome To BYC! It is usually best to wait until the younger chicks are about the same size as the older ones, and then introduce them gradually, a period of time separated by wire usually works well, ie if you can separate your coop/run or put the younger chicks with their cages inside. That gives them time to get used to each other and kind of establish a pecking order. There is a good article in the Learning Center on combining flocks https://www.backyardchickens.com/a/adding-to-your-flock You might like to check out the BYC Learning Center, lots of good articles on all aspects of chicken keeping in general you might find helpful. https://www.backyardchickens.com/atype/1/Learning_Center
