Croquet
Croquet is a classic outdoor game that dates back to the 1300s. Croquet sets are available at many sports stores and big-box stores, and range in price from $20 to more than $5000, giving you a wide range to choose from. What's fun about this game is that it can be played by young and old. If you're playing with young children, you can agree to form a team of one adult or older child per mallet so the two can play as one. You can even create your own courses where wickets are not placed according to the regulation rules but wander down paths, up and down hills, or wherever your imagination desires. Sites like Toycrossing.com have the official rules posted, but you can make up your own rules as well.
Capture the Flag
This is an outdoor game to play with friends. Best yet, it can be played by young and old. All you need is a little room, two flags on posts, and the desire to keep your flag from getting captured. You and your friends can form two teams that will do their best to capture the flag from the opposing team. If you live in the country, you can make the game even more challenging by placing the flags quite a distance from each other. If you don't have a lot of space, you can make up rules to make the capture of the flag more challenging.
Scavenger Hunt
This game, like capture the flag, is more fun if played outdoors where there's a lot of space. However, this game can be played anywhere outdoors---even in a small public park. In this game, you and your friends form teams and are given a list of things you must find within a certain time. A more-challenging list might include clues in the form of riddles or rhymes. One delicious idea is to have a scavenger hunt where players must find edible foods in the yard such as sour sorrel, dandelion greens, Japanese Knotweed and purslane. Just make sure you wash the greens thoroughly before eating them.