Throwing a themed birthday party can be a lot of fun, but it also comes with a certain measure of risk. Not every theme is going to go over well with everyone on your guest list. The biggest mistake you can make when planning a theme is forgetting who your audience is. A kid's party that's so long and complicated that there are big lulls between games and activities is never a good idea. Kids need a constant flow of entertainment. If you have a high count of "stick in the mud" family members, something requiring too much participation is a bad move. Before you plan your next themed birthday party, take heed of our warnings.