Going to birthday parties has always been great fun for kids. When I was young I’d wear a pretty party dress and my mother would take me to the birthday kid’s house, with me proudly carrying the wrapped gift. Then we’d put on paper hats, play games, and eat cake and ice cream while the celebrant’s father took home movies as we shyly waved at the camera. A generation later things were quite different. The birthday parties I took my son to were usually themed...