It might sound silly, but I want to give credit where it is due for the other cats (and dog) that help raise our kittens.  Not only do we raise our kittens in a home environment, but they also are raised around other animals.  Our kittens grow up knowing that every person and animal that they meet is a potential friend!  They still may need time to get used to a new person or animal in their environment, but they do know they aren't the only one!