If you are getting baby chicks, you can't put them out with the rest of the birds right away. They need to kept warm, with a heat lamp, or something as simple as a 100 watt lightbulb. They need to kept that way until they are fully feathered, 10-12 weeks. After that you can start slowing integrating them in with the others. IN our hen house, we have a small area that is seperated by chicken wire from the others so they can get to know the babies.
Then we let them out into the coop with the others for a few hours at a time and see how they do. If they get picked on, we don't let them out for so long, but we do keep giving them visiting hours with the flock. Usually at about 15-17 weeks they are fine and integrated. No problems yet with that method!!!!