We pen our kittens out where we want them to stay. They stayed penned until they are comfortable with me and their new surroundings. Usually a week or two. I than let them out under supervision, and pen them up at night. After a while they are left out. Usually after 3-4 months. Mine are in a secure shed with a kitty door. They are fed in the same place daily, and have beds and heated houses in the winter. They generally don't start being serious hunters until after 6-8 months of age.
The only problem with barn cats as you have to expect loses at times. We vaccinate, and spay and neuter. Our 3 currently kitties are wonderful hunters. I'm getting 2 more in 2 weeks to eventually help out.