I know this isn't technically a boomerang, at least in the traditional shape, but my 6 year old and I had so much fun with this cereal box boomerang!
We played with them outside, and between the wind and the boomerang itself, they were completely unpredictable. It was entertaining to say the least for both of us to throw our boomerangs and try to chase them or predict where they would go. It was a treat to have everything work and have them come right back to us.
All you need is a printer, cereal boxes and scissors. You can find the template at Angelfire. Thank you ikat bag for the fun idea!