Jim;
I've looked at this image several times since you posted it, trying to concisely decompose what I find rather captivating about it.  Here's what I've concluded.
1.  Gesture and expression.  That subtle head tilt and Rowan's solemn, actually rather stern, expression are eye-stoppers.  As I see the midday sun I realize he's squinting in the glare.  But it seems that he wants to be somewhere else and grandpa is being a pain in his ass with the camera.  It's excellent.
2.  Nose Band-Aid.  Just a touch of mystery, even to grandpa.
3. Big head.  That 90-degree pose, Rowan's small upper body and his protruding ears make his head appear just slightly abnormally large.  This accentuates the effect in #1.
4.  Dark shirt.  A white tee blasting fill up wouldn't work as well.  I must say, however, that I'd consider cropping the shirt's chest design.  Maybe, maybe not.  Not sure myself.
5.  Soft focus.  It's slightly distracting but in this case it creates a feeling between candid and formal. 
Nicely done.