How old do my chicks need to be

[kunas]

How old do my chicks need to be before adding them to my current flock, flock consists of RIRs and brown and white leghorns all hens thanks Ron

 

[crait]

Hens should be easier to mix babies with, but you need to wait at least 6 weeks. At least!
You don't want your babies outside to die because of chilling. I'd wait 8 or 9 weeks to be on the safe side if you can.
You also need to ease them into one group. I'd say get another cage or something and put them outside in it. Let the girls see the babies a few days and then let them roam around a few hours a day. They'll get pecked but that's okay. They should be old enough to withstand it. My rooster is strong. He ripped part of the crop off of my baby whenever she was 7 weeks old and she nearly died. Thanks to the folks here on BYC, she was helped in time to be saved. Hens usually don't peck as much as roosters and are usually weaker, too. Whenever all the girls are roosting, and you feel comfortable, put the babies with them to sleep. The girls will be too busy trying to get some sleep they won't realize they've been had.

Good luck!