Classic Kids Games
Have the kids engage in classic yard games. For tag, establish a home base and choose one kid to be "it" and chase other players. The "it" kid covers her eyes while the other kids hide. Once the "it" kid tags a player, that player becomes "it" and takes over chasing duties.
Hide and seek is another classic game your kids can play. Have one kid cover her eyes and count to 20 while the other kids hide somewhere in the yard. Once the 20 seconds is up, the "it" kid says, "Ready or not, here I come" and looks for the other kids. If the seeker finds someone, the found kid becomes the seeker.
Get a rope long enough for all of the kids, mark the center of the rope with a flag or tape and have them engage in a tug-of-war. Divide the kids into even teams and have them grab either end of the rope. Have the two teams pull the rope toward them, until one team has pulled the middle of the rope over a particular line. If one side is notably stronger than the other, the losing team may end up tumbling onto the opposing side.
Tossing Games
Horseshoes remains the ultimate tossing game for yard fun. Put a post in the ground and establish a distance far enough between it and the kids. Award points based on how close each kid's horseshoe comes to the post. Players score a ringer if their shoe wraps around the post and stays.
Younger children may find more success holding a washer rather than a horseshoe, so they may have more fun with washer toss. Divide the kids into two teams and have them pitch round washers into wooden boxes.
Set up a three-rung ladder for hillbilly/ladder golf (you can get this game at Walmart, among other outlets). Divide the kids into two teams and have them toss bolas (two colorful balls held together by rope) at the ladder. Award points based on where a player hooks his bola (three points for the top rung, two for the middle and one for the bottom). Whichever team scores exactly 21 points first is the winner.
You also can divide the kids into pairs to play water balloon toss. Have the pairs stand close to each other for the initial balloon tossing, and then after each catch, have them take one step back. The last kid to toss the balloon before it bursts wins the game.
Other Games
If you have a swimming pool, have your kids play Marco Polo (one player moves around the pool with her eyes closed, in pursuit of others). You also can set up a volleyball net in the pool, or have the kids play volleyball or badminton on the grass, the latter with or without a net.
The kids also may enjoy going on a yard scavenger hunt. Give each kid a list of 10 items to find in the yard, whether regular outdoor items or ones you placed in the yard yourself. The kid who returns with the most items wins the game.