The Shishkaball Ball-Drop Game is fun for kids (and grown-up kids)! Check out this list of 13 DIY backyard games and play structures from This Old House.
Use pool noodles to make fun outdoor games for the kids.: Cheap summer party ideas for kids
Washer Ring Bucket Toss Game: This game - in which players attempt to toss washer rings into buckets - is as easy to set up as it is fun to play.