Should you host a Summer Olympics? Absolutely!

How We Organized It:

We brainstormed several outdoor events, how many people would be needed from each team to play that event, and all the supplies needed. We set up all the equipment before the students got there to save time.

We split our group into three different teams. We gave the students a list of the events we had planned for the night. Next to each event we wrote how many students from each team were needed to do that event. So each student was able to pick what event(s) they wanted to partake in. We had enough events for most students on teams to be in 2 or 3 events and we required students to choose at least 1 event to play in. We kept track of 1st, 2nd, and 3rd, place for every event and then added up the points at the end to see which team took home the "gold".

We spray painted a boogie board gold and had the people on the winning team sign it. It hangs in our youth room year round and is waiting for the next summers winners to sign their names on it. Alternatively, you could buy or make silver/gold/bronze metals or spray paint some small wreaths gold and use them as crowns.

Our Events: (feel free to modify any of them or invent your own!)

Javelin throw: one person per team, we used PVC pipe and did this in a field. After each person threw the pipe, we marked the spot it landed with a stick and recorded who threw farthest & what team they were on, who threw second farthest & what team they were on, etc.
Watermelon Shotput: one person per team. We have some strong guys in our group so we bought big ol' watermelons. You can totes buy the smaller mini ones too though.
Pool Noodle Hurdles: one person per team, put wooden dowels into the ground (dowels are cheap and can be found lots of places) one pool noodle-width apart and attach the noodle by pressing it down onto the wooden dowels. I think we made four hurdles. Don't make em' too tall and test them out yourself to see if they are actually jump-able. Send each team's representative one at time to go through the hurdles and time them with a stopwatch (or set up the course with four lanes so students can go at the same time.) Add a one second penalty every time a hurdles is touched.
Blindfolded Fencing with Pool Noodles: One person per team, Blindfold each contestant, give them a pool noodle and let them go after each other. When someone gets hit, they're out. Last person standing wins. To make this easier on the blindfolded contestants, we had all of our students from all the teams stand in a circle around them -- that way they didn't have to worry about wandering off too far.
Triathalon: One person per team. This was the most fun event to watch. Place a kiddie bike at a starting line. Have students ride the bike 30 feet (or more) to a kiddie pool filled with water, get off the bike, and roll in the pool 3 times. From there, have student sprint on foot to the finish line. Time each student. Best time wins. Provide 3 towels for these contestants as they will be soaking wet afterwards. (Also we made a general announcement when we advertised for Summer Olympics that students should wear clothes that could get wet).
Target Practice: Four people per team. Get a waterballoon slingshot (sold at Target in the summertime -- or online) and have a bunch of waterballoons filled. We had 3 students working the slingshot (one holding a side taught and the other loading and shooting the ballons). The 4th student was several feet away with a bucket, catching the waterballoons that were shot. Every balloon that goes inside the bucket counts as a point, each team has 10 balloons). Be sure to make a shooting line they students must launch behind as well as a line that the catcher must stand behind (30 or so feet out from the shooting line).
Volleyball: Since we had three teams and wanted to keep things fast paced, we didn't have time to do traditional two-teamed volleyball games. So we made our own court by taking athletic spray paint and made a large circle on the grass (big enough for 3 teams to fit inside). Then we split that circle into thirds and painted lines to mark each section. We didn't use a net. Instead we had a referee throw the ball into the air. If it landed on your team's portion of the circle, you were given a negative point. If your team hit it out of bounds, you were given a negative point. The team with the most negative points got last place. The team with the least negative points got first place.
Waterballoon Barrage: We played this game during Water Wars and so we didn't actually include it in our summer olympics but you definitely could. Give each team a bucket of water balloons. Like 100 balloons each. Don't worry, water balloons are very biodegradable :). Then have the students throw water balloons at each other. Each time a student is hit, their team loses a point. Assign a leader to each team that will keep track of the number of times a team is hit with a water balloon. If a student tries to catch a water balloon but it breaks in his hand, that counts as a hit.
Popsicle Eating Contest: You don't want your kids to throw up and neither do we, how about... whoever eats 3 Popsicles first wins? You can use any kind of popsicle but we didn't want any with sticks so we used those fruit juice push pop things. Ice cream sandwiches might be fun too.

Our students really enjoyed this event and I hope yours do to. Check out this promo video Ruby made to advertise this event and consider making one for your group too :)