Looking for advice on mixing groups of chicks

Looking for advice on mixing two groups of chicks. One group of 12 5-week old chicks (mostly female but there might be a surprise boy in there) and a group of 6 2-week old chicks of which 3 are definitely boys.
They all need to live together eventually, and I'd rather mix them now than later.

If they were mine I would only mix them if they were on an open yard. Three weeks is quite a size difference for chicks, it won't take much for an older chick to do a lot of damage to a smaller chick. It would be better to mix them later when the size difference isn't as much a factor.

Depends on the size of you area. I have been successful introducing a hugely diverse group of ages and species simply because they have an entire barn as their coop and 40 acres as their run.

This is a pic of my grow out pen 2 years ago. There are chickens, guineas and peacocks in it, all different ages. I had no issues. It was a large area.

If you need to do it before they catch up in size (3-4 weeks would help the little guys out), you can make a "creep" of some sort where the littler ones can get away from the big ones and have access to food and water and shade. I've made one out of a hoop of concrete reinforcing mesh, with a wrap of chicken wire an appropriate distance off the ground so the littles can get in, but not the bigs. Shorter than you think, chickens can squash themselves lower than it seems possible to get to something they want (like hens after baby chick starter).

I also suggest waiting until the younger chicks are physically big enough to defend themselves, or safely escape.... have as much coup and run space as possible. There will be some rearranging of the pecking order. It could get ugly. I watch mine for a few days after combining, making sure the lower birds aren't being harassed to much.

- L. Daniels

Thanks y'all. Right now the "big" birds are in a kiddie pool out in the breezeway and the "little" birds are still in a brooder in the laundry room. They're all waiting for either their coop to be built or for my to send the "fat birds" to freezer camp so all these guys can move into the tractor.

I want to combine these two because I currently have FIVE DIFFERENT groups of birds all its driving me nuts. Guess I'll stick it out a few more weeks until the little guys are a bit bigger and no chick fluff.