you can ...
Football, swimming (install a small plastic swimming pool), etc.
You could play hide and seek in the backyard, ride a bike, go on a walk, and many other things.
You could get a magnifying glass and check out the insects and things in your backyard. You could play sports. You could invite friends over and have a scavenger hunt.
you would have more fun at a dignified backyard barbecue
fun
Things in the backyard include flowers, fence and flies.
Because they both have active things and also they are very fun
There were some great things to do for free or inexpensive family fun. Some ideas they had were family game night and camping in one's own backyard.
Ray moved the hose.
Ray moved the hose.
One fun thing would be capture the flag! some other things are: tag, hula hoop contest, or hide something like a Frisbee in your backyard, and have some people try to find it!
Fun birthday games are active things, like scavenger hunts. You could also do bean bag tosses, croquet, or bocce.