Rick Riordan's The Lightning Thief
Since this is shaping up as the new Harry Potter-esque film crossover, I thought I'd check it out. Pretty fun. He also makes an interesting point about western civilization in the book that I've just been making while teaching writing (and will make again and again.) His point, though, seems to imply that western civ rules the world period, no critical thinking about it. So a bit problematic.
But given that you want to update Greek mythology for kids (in goofier-than-Gaiman way) I think this is a pretty good try.