12 week old chickens, when can they mingle with my existing adult flock?

[ChickenLady2012]

I currently have (4) 12 week old chicks and an already existing flock consisting of 1 RIR rooster, 1 Black austrolorp hen, and a RIR hen.... at what point can my two flocks mingle together ? The big chickens have a nice large coop and free range on our 2 acres,currently the little ones are living in a coop in our barn with access to a small outside run thats is with in the run/coop area that the big chickens have. We moved the small chickens to the barn a few weeks ago, and by that nature the big chickens have seen and been exposed to the small ones thru the fence..... we have not allowed the the two flocks to have direct contact w/ each other. My rooster has shown alot of interest in the little girls, he will often come up to the run and do his little tap dance and scratch and try to find food for them, he will come running when he hears their clucks.... It appears he just wants to take care and love them like he does with my 2 big girls.....My one big RIR hen at first got all huffy about the little ones, but now since a few weeks have passed she seems to have mellowed out.... I'm excited to have all my girl together but have never done this before.... any advice is greatly welcomed...

 

[Den in Penn]

You can leave them free range together now. While they free range the young ones will have plenty of room to avoid the older ones if that is necessary. Just allow them to return to their own coop for a while till they interact with only a few get out of may way pecks.