Chicken chicks, or ducklings?
All flocks are different. Even the time of year can cause them to act differently. I would suggest starting with an area where the 2 groups can see each other, but not touch.
Then move to supervised visits, when you can watch to see how the older ones react, and be able to break up any fights
Also provide a place where the little ones can escape from the bigger ones, if they happen to start picking. Some folks just use a box with a door cut big enough for the little ones, but small enough that the older ones cannot fit through. Put the little ones in it, and let them venture out on their own. They will realize it is their safe space.
But overall, the sooner you socialize them, the better it will be. They usually learn their place in the pecking order fairly quickly!