Should have Known better!!!!

don't feel bad, I tried sort of the same thing. I had three silkie hens in with young Copper Black Marans, five roos, three pullets. Over time, the roos started treading the poor little silkies and I made a pen within a pen, that the silkies could go in and lay their eggs and have their adult lay pellets and clean water unmolested and get away from the large roos. Well, they didn't stay in the pen much on their own and the roos nearly wore their backs down in a week and I was afraid I was going to find one dead, so I put a roof on the little pen, and closed them in it. They didn't like it but at least they are safe and I don't have to worry about them any more. It is funny, now that they are safe behind the bars, they charge the roos and peck at them when they can through the wire which is two by four inch holes. The roos must have been pinched a few times, because when they see the silkies put on their game face, by golly they scatter!

 

I've tried making refuge available to smaller chickens with entrances only large enough for them, and had very little success, unless I've put it in an out-of-the-way location. The smaller chickens have to slow down to fit through the small entrance, which gives the pursuers a chance to catch up to them. And when the small chickens feel the pressure of pursuit, they flap their wings in the chaos and can't fit through the entrance.
I lost a chick in my experiments It was very sad.
I'm very sorry some of yours have gotten hurt.

 

I always wait to add chicks to the older flock when they are almost the same size and can defend themselves....adults will and can starve out younger chickens by not letting them eat and drink...always make sure there are 2 or 3 feeders and waterers in the coop and run to make sure this does not happen...