Ha! I'd suggest cropping this so your son is left of center and the toilet's right of center - it would feel more balanced. The center is a good place to avoid, generally.
This reminds me of a list of things you learn from 5-year-olds. There's a whole series of "if you can't find X, look in the toilet." Including keys. :)
Hee hee, gave me an instant chuckle. Fortunately, I've never had this happen. Maybe because I don't have kids :-)
It doesn't look like you took too much time to set the shot up - has a candid look (not necessarily a bad thing, especially given that the action is naturally a spontaneous one). I do think a fill flash on your son's face or directional light highlighting his features would have bumped you up a bit. I also find the gargabe can a little distracting in the front.
Overall very cute, though.