Bean Bags
Bean bag games are like a kid-safe version of backyard horseshoes. Though bean bags are softer than metal horseshoes, they still can hurt someone if thrown hard. Kids should never be allowed to throw bean bags at each other, but only at target holes or tic tac toe yard games.
Camp Out
For kids who want to get the same feeling of camping out in the wild, but without leaving the safety of their home, they can spend a night in a tent in the backyard. All of the camping supplies can be included in the activity: mosquito spray, s'mores, flashlights, sleeping bags and even scary stories. A regular tent can be used, just make sure that the house is always available for the kids in case they get scared and want to sleep inside.
Swing Set
Kids don't have to go to the park playground if they have a swing set of their own in the backyard. The play sets may also include slides, monkey bars and club forts. If you have a tree in the backyard with strong branches, you can tie a rope and old tire from it. One other fun addition to a backyard playground is a sand box, which kids enjoy building sand castles in.
Races
If you're looking for organized games that kids can play in the yard, one of the easiest and cheapest things to do is racing. Relay races around the edge of the yard are fun, but setting up a makeshift obstacle course is usually more fun for younger kids. Throw down some old tires, a sand trap or monkey bars, and the kids will expend as much energy as possible. This is perfect for a birthday party activity.
Water Fun
Of course, this is a summertime mainstay, but setting up water games in the backyard is wet and wild fun for kids. Make sure they put on their bathing suits first, and then either set up sprinklers or Slip 'N' Slides for hours of activity. Even if all you have is a green garden hose, kids will have fun spraying each other. But add a kiddie pool, squirt guns or buckets, and you'll get one of the craziest backyard parties you'll ever see children partake in. Just make sure that towels are on hand by the time they're done. A wet kid in the house can make a quick mess of the place.