advice?

Hey, I’m doing this for a kids magazine; the kid won a prize where he gets to have his comic redrawn by a ‘professonal comics person’. I’m trying to knock it out fairly quickly, but I’m having trouble with the colouring… I want to make it bright and cheerful, but it looks pretty garish. Any advice for how to make this better? (Just ignore the rather dodgy narrative order of the second panel, I thought I’d stick pretty much to what he’d drawn.)

Click to enlarge:

(Here’s the original)

Edit: Thanks so much for your help, guys! Just sent it in!