I brood using the mama heat pad for warmth. Chicks self wean from the heat and by three weeks arent using the heat, but view it as a comfort source, hanging out on top of it...it is removed at 4 weeks Chicks start in an area of the coop sectioned off by a wire panel. They see adults and adults see them from day one. At three weeks, a small door in the panel is opened, chicks fit/ adults don't. Chicks can go in and out, escaping to "safety" if they feel overwhelmed.
At this point the hens are accustomed to their presence, like they would be if one of them had hatched and 4aised them in the flock. Cursory pecks happen, ie when chicks forget their place in things, but hens mostly ignore them. By four weeks the panel 8s removed, the brooder space is once again just part of the coop and chicks are just part of the flock.
These threads and articles talk about the method(s)
https://www.backyardchickens.com/ar...rt-raising-your-chicks-outdoors.71995/?page=2
https://www.backyardchickens.com/th...er-picture-heavy-update.956958/#post-14882145
https://www.backyardchickens.com/threads/integrating-chicks-into-flock-at-4-weeks-old.1159151/
This shows the complete disinterest the hens have in chicks when integration us occurring
And the interaction between a hen and a chick who is instigating trouble