Where have they been brooded? If they have been brooded within full view of the main flock, you could start introducing them in another 2 weeks or so. They aren't fully feathered and generally still require supplemental heat at 2-3 weeks of age unless your low temperatures are never below 75F. It also depends on your coop/run arrangement and how much space and other resources you have. The more space the better. Some place for the littles to hide and get away where the bigs can't get them is ideal.
To add to this, they could possibly be introduced now, if they've been raised so the flock has had some time to see them, however they'll still need some level of protection. Even if heat isn't an issue (i.e. you're in a hot climate) I wouldn't toss them in quite yet. I started letting my chicks out around 2 1/2 weeks to meet the hens by making a chicken wire enclosure around their brooder, letting them explore that for a few days, then putting the chicken wire up on bricks so the chicks could dart in and out under the gap. Plus I added extra obstacles to the run for more hiding spots. However they remained in the brooder at night until 4 1/2 weeks and didn't join the hens on the roost for another week after that. More detailed info: https://www.backyardchickens.com/articles/short-on-time-recycle-a-prefab-brooder.73985/