Shoot Out
What boy doesn't like shooting games? This one is simple enough to play with most age groups. Line up empty aluminum cans and have the boys stand behind a line and aim at them (one at a time) using squirt guns. Each boy gets to knock over as many as he can until he runs out of water.
You can also play this game with small plastic bugs or snakes and line them up on a hard surface such as a table or sidewalk. Allow the boys to shoot at their prize and if they move it, they get to keep it. Rotate turns often so everyone has a fair chance at the prizes.
It's a Ringer
If you already have a theme for your party you may be able match this game to it, such as using sporting equipment (bats and golf clubs) or swords, toy rifles and light sabers. Be inventive if you like, but it is doubtful the boys will mind if you use something as simple as a stick. This ring toss game involves teams of two boys, one with the rings and the other with the catcher. Race to see who can get the most rings on the end of the stick in the shortest amount of time; whichever team wins gets a small prize. You can play this game in a number of rounds until the boys tire of it.
Remote Control Racers
If you have remote control cars around the house or have a chance to borrow some for the party, plan a car race for your party complete with a checkered start flag and finish line. Design the course however you like, with obstacles or tight squeezes, inside or outdoors, and have the boys race in teams to be eliminated. The final race will be with the top two contenders.
Balloon Stomp
This game can be played a number of times and will appeal to the sometimes destructive nature of little boys. Blow up enough balloons so you can play this several times with your guests and attach one balloon each round to the child's ankle with a string or piece of yarn. The object of the game is to stomp out everyone else's balloon while keeping yours safe and intact. You can offer prizes for the winner but more than likely they will have just as much fun without them.