Howdy SilkieLady6
I am not sure if there is a fast way in which someone will not get hurt, but I will be interested to hear others thoughts also.
For me, integration is usually a gradual process and can take a couple of weeks.
If you put the little ones in with the big ones not only will they be picked on, they are in unfamiliar territory and do not know the good places to hide etc. The larger birds may also bully them away from the food and water.
The ‘look but not touch method’ is the one I have used with good success; keeping them separated with wire where they can see and communicate with each other without anyone getting hurt. Free range is also a good time to allow some mingling under supervision.
Does your coop have a run or are they total free range? If you have a run, is there any way you could divide it so the smaller ones could be in there during the day but back in their original run for sleeping?
Just my thoughts, but if you do not want them to get hurt, I would look at some way to temporarily increase their run size while also working on an integration plan in the main coop.