I like this one the best out of the set. It has a nice use of thirds and the kid has some interaction.
Your son's set is kinda blah. When I shoot kids that don't want to smile I get them to laugh. In you case I would talk to him while shooting, ask him about the girls in his class that he might like. Say something stupid to get him to smile. Or go the opposite and get them to be more model like
Out of the set this one I like. The angle is different. Composition is nice.
In the last two sets I would continue practicing framing the shots. You shot every thing with your son at aperture f/2.8. Eventhough you got some nice bokeh, his face wasn't sharp.
The right side of his face is out of focus
Check out Jared's 5 minute tip on portraits.
http://www.youtube.com/watch?v=SFzkz8029Ls