When I was much younger, I was best friends with a girl who fit the description of overparented kids to a T. She was in a million activities, everything from soccer to ventriloquism lessons (no joke), and whenever she showed the slightest interest in anything else, her parents started looking into getting her into some class for it. They adored her; she could do no wrong in their eyes, and so they indulged her every whim.
She wasn't a bad kid. She was very sweet and a good friend, but she could be grating. Any setback in school--a bad score on a test, someone else's poster being prettier than hers-- was a disaster. Being 'it' for too long in tag inevitably resulted in her quitting the game. At the tender age of eight, she taught me the reason so many adults let children win at board games. The day was not complete until this girl had cried at least once.
I wouldn't say she was unhappy, exactly, but most of her friends were kids she'd met through playdates her mother had set up with other mothers, and she often said to me that she wished she had as much free time as I did. It was really too bad, because there were a fair number of other kids our own age in our neighborhood, and those of us who weren't constantly being shuffled from one organized activity to another hung out a lot together and got to be good friends.