Kids' birthday parties are essentially a trial by fire for new parents. As if the legion of boisterous children wasn't bad enough, you've also got to deal with unpredictable weather, party games that invariably don't work and baking a cake that looks like a cartoon character (as opposed to a malformed blob.) But arguably the most stressful moment is the whole "pressie opening" fiasco -- especially if you have an unruly kid. Here's a simple tip to make things run a little more smoothly.