Equipment:
A super-soaker or water pistol.
Darts: regulation, velcro, koosh or other.
Pool: regular or kiddie.

Description:
The modern pentathlon (shooting, fencing, swimming, equestrian, and running) can be easily transformed into today's backyard pentathlon with a few minor changes.
Shooting: See who can reach the farthest target with their super-soaker or water pistol.
Darts: Depending on the ages of your children you can use regulation darts and a dart board or velcro or koosh dart games (made for young children and found in any toy store).
Swimming: Best original swim move in either the kiddie or regular pool.
Jumping: See who can jump the farthest from a single starting point.
Running: See who can run the fastest around the house, up the driveway or around the block.
Determine a point scale (1 to 5 for example, 5 being the best). Points are given for each individual event and the individual with the most points after completing all events wins. You can give out prizes for each individual event as well as the gold medal for the pentathlon winner!

Other comments or suggestions:
You can make your own gold, silver and bronze medals with construction paper and ribbons.
Or rewards can be food based: ice cream, cookies, and chips.
Or rewards can be chore based: 1 free night no dishes, 1 free day of not making your bed, 1 extra hour of TV time.
Have fun with it. Let the family decide beforehand what today's Olympic rewards will be.