Banana is an adorable, smart, funny five and a half year old. She is also an only child, and she is beginning to exhibit--regularly--some of the symptoms of Only Child Syndrome. She forgets to share, particularly when she is tired, and sometimes she insists on dictating how other kids play with her. "No, you have to color the skirt purple, not blue," that's the sort of thing she's been known to say recently.
Based on some reading I've done, part of this behavioral development in the shift from five to five and a half--where well-behaved kids become a little bossier and a little more determined to show what they know. Part of it is clearly the fact that she is an only child, however, and conversations with a close friend who has spent a fair amount of time with her recently bear this out; she hasn't always played with the others in the way that we want her to.
As a recovering only child myself, I watch some of this with a little trepidation. Being part of community of parents and kids helps allay some of the potential ME/MINE problems, but I am beginning to realize that I have to pay close attention to head off the dreaded doesn't play well with others or share problems.