A sports-themed party is a great way to celebrate your son's birthday. Not only are they easy and inexpensive to put together but the kids will absolutely love it.
This theme really lets you get creative. You can either focus on a specific sport that's in season (if it's a summer birthday, throw a baseball party, football for fall, etc) or do all at once! Making a "ticket" invitation on the computer is simple. The information should include the date, start time (kickoff, first pitch) and location. Finding athletic clip art will be no problem.
You can get your hands on a sports-inspired cake easily as well. Most supermarkets will sell cakes with a variety of athletic images on them, so take your pick! You can order personalized candy wrappers that boast your little one's name as well.
If the party is outside, your job is simple. Just have the kids play tee-ball, touch football or really any activity that will get them running around. If the shindig is indoors, you can have the children watch a sports movie like The Sandlot. A "tailgate" party with Cracker Jacks, nachos and a sub will keep the kids happy and full.