Best friends forever. Preschoolers are very interested in what other kids their age are doing, and in getting along with them. Until now, they haven’t had the social skills to take relationships any further. (Most children don’t really understand the idea of sharing until around age 3.) But with a growing ability to understand and express emotions, your child has likely started to develop some real friendships. She may even call one or two kids her “best friends.”
“Mayo Clinic Guide to Your Baby's First Year” by Mayo Clinic.
“Caring for Your Baby and Young Child, Birth to Age 5 (5th Ed)” by the American Academy of Pediatrics.