Integrating 5 week old pullets into flock

Hi chicken tenders,

Please advise, I'm freaked out after trying a meet&greet between 5 week olds and 1 year olds. 7 babies, 4 grown hens. The chicks have been with the hens in their space but in a crate with their brooder plate and food/water. Now they're getting too big for the crate and I need to let them integrate.

To cut to the chase - babies had the run on their own, we're getting comfy and enjoying some dust baths. Brought the hens in and most of them ignored the babies, but soon the lowest hen in the pecking order began to chase the babies around, pecking and getting mouthfuls of feathers. No blood, but she did not seem apt to settle down. We wound up putting the babies back in the crate for the night, unwilling to leave them to fend for themselves.

We are prepared with a small door into the crate so that the chicks will be about to come and go and the hens won't be able to fit into it. But closed it up for tonight because I don't want them getting pecked to death!

What can we do?? Do we just need to keep them separate until the babies are older?