Uh oh! Kids are messy little creatures; good thing they're cute.
The Carpet & Rug Institute's spot removal guidelines can be found
here. For chocolate, they recommend that you act quickly and not let it dry (too late for that, I know). After that, test your spot removal agent, use a white cloth (so you can see if any of the chocolate is coming up), and then keep at it as long as you're getting lifting of the spot. Don't scrub!
Good luck!