Is there any way you can separate them for a couple of weeks so they can see each other, but not touch each other? If you can, this is best. Some people quarantine new birds for a couple of weeks in a completely different area to make sure there is no sickness before mixing them with the existing flock. If this friend has been raising the adults and you know they are free from illness, you still want to let them adjust to each other a bit.
When my chicks outgrew their 'nursery' in the coop, I provided a 'run' in the larger run that was up off the ground enough the chicks could get in and out, but the big birds couldn't get in and I put food and water in the run just for the chicks. It kept the adults out of the chick feed, and allowed the babies somewhere safe to go if they are getting picked on. Someone else on this site suggested it and it works great!