For my twins 10th birthday party we chose an Olympic Theme. My husband spray painted a small running track (with lanes) on the grass in our back yard.
Each guest was asked to dress in sports atire and tennies. We spent most of the day playing relay games like, filling a cup with with water using a spoon after walking 10 feet. One favorite game, costume exchange, where the first person in each relay team dresses in the costume given (our costumes was a very big mans suit (I got from a garage sale), a derby hat and boots, the other team was a womens had a moo moo (it was my mom's) and dress shoes (no high heels). Each team was to dress run a distance around a tree and then take off the costume and the next person in like puts it on as fast as they could, then repeat til they've all had a turn. The first team to finish wins. The grand finally game was the team relay race (we did this one a couple of times) where each team member runs a distance around the track and instead of passing a baton they would pass something to wear (ex: 1st runner starts off running with a hat on, while the 2nd runner waits wearing a Hawiian lay, the 3rd runner is wearing a huge pair of shoes (clown shoes or water fins are the best if you have them) but our's ran with slippers, they are hard to keep on when your running, the 4th runner is wearing a pair of those huge sun glasses, and the 5th runner is wearing somekind of water tube around their waist. Each runner then passes their item to the next, so that the last runner is running a couple of laps (depending on the track size) in the hat, glasses, lay, shoes, and inner tube, and has to pass the finish line wearing it all. For favors we gave all our runners plastic olympic medals, little bags of chocolate that looked like money, and ribbons for good sportsmanship. We made a pinata with the Olympic symbols on it and filled it with candy, and the decorations were all different colors and we colored a banner "Welcome to our kids names Olympics." All my kids friends love the birthday party's we throw and had great fun!