You should definitely quarantine for 30 days if they are brand new chicks to you. (If you'd been raising them already for 4 weeks at your own home then they are already quarantined
I did an integration recently that was similar and after the quarantine period I let the babies out with the bigger ones for short periods of supervised time. You can also section off a part of the coop/run for them (make a divider with holes small enough that the babies can fit through but not the bigger ones). Many people suggest putting them on the roosts at night, which is how I did the final integration but that was after quarantine and introductions were over. Now my babies roost with the bigger girls. They are still certainly at the bottom of the pecking order and the other chickens pick on them a little, but they have never been truly hurt. This is a very scary time though as they could easily be killed by the older birds.