Wow, I just fell out of my chair. Anyway I'll work from the top down.
What for?

Hat:
-Define you light source dont out line it with a darker shade if its sosposed to be lit
-Propeller seemed to high up
-the shapes on the hat needed to be more triangle like
Thanks, it does look better now. You utilized colors better than I did

.
Hair:
-The front of the hair is very unnatural, It looks as though it just flops down.
Well, I don't know if adding more..whats the word..locks of hair improves it or not. Need more opinions on that.
Face:
-Theres no mouth! He cant breathe. lol
-More shading and also needs highlights
He's not supposed to have a mouth. I had lots of trouble shading the face. Yours is better, but I think that I need help on the eyes, and making them more cutesy and boyish.
Shirt:
-The arm creates shadow over the body, darken it up.
-Put highlight on bolth the arm and shirt/sleeve.
Erm, now the torso looks like it has chunky noise. I dunno, just me. I'll try to improve it. I don't even like the anatomy much, but not sure how to change it, and keep it cartoonish and caricatured.
Shorts:
-Very square
-Need highligts
Yeah, I realize the anatomy is very bad. Thanks for the help.
Feet:
-Look rather big and round
They are supposed to, but maybe I could make them slightly smaller and rework them somehow.
As for color I would just use what you got there its always fun and enjoyable to see what you can do.
Here:

I outlined it in black so it can stand out againts the back ground.
Oh and good luck with the GM competition.
Thanks for all the help. I need more opinions/help though. I'm kinda dissatisfied with the whole thing, as I want it to look dynamic and more 3dish. Also, I'm working on not adding any outlines, especially black, and I think that it might detract from your edit as well. But thanks for everything! Will try to take things into account, and will post an update later today, I think, addressing those issues.
Sokota