Sometimes you just gotta tell a kid he's a ninja...
I've grown up surrounded by kids. I'm the oldest of four and my youngest brother is 11 years younger than I am. But even further than that, both of my parents are the youngest of seven kids; so by the time I was conscious, my oldest cousins were having kids of their own making every family get-together a circus freak show. Even my work experiences have been geared towards working with kids in some capacity-first a swim instructor, then a dance instructor, then a teacher, and now a kid photog. Sprinkle in some babysitting and nannying here and there, and you have my resume. Needless to say, I get kids. They aren't going to sit pretty and let you take nice headshots of them all day. They won't allow you to place them where the best natural light is. In fact, they will probably go out of their way to avoid your camera because that would simply make life easy and uninteresting.
Kids will make you work for it.
The beautiful part about kid photography is that, when done right, it is the truest representation of the little person you are shooting. When they are comfortable and in their natural habitat, their personality and mannerisms shine through better than you could ever pose them.
So sometimes you gotta tell him that he's a ninja and then roll with it.