The chicks might follow the big girls in when they're ready or you might have to put them in when the time comes.
It's essentially impossible.
This is why I feed my entire flock on all-flock feed since I have males and mixed ages.
I don't wait.
Once my chicks leave the brooder I move them to the integration pen inside the main coop -- where they spend a week completely surrounded by the older birds as they all get used to each other.
After a week I open the chick-sized doors to let them roam as they choose -- while...