This is a fast and fun activity for kids studying Australia, or perhaps as an Australia Day activity. It lends itself as a group or class activity, too.
Cut a boomerang shape out of brown card and use bright coloured paper shapes, pipe-cleaners and whatever else you have to hand to decorate it.
Older children can decorate their boomerangs in aboriginal style using poster paints and a wooden stick, chopstick or pencil dipped in the paint. Have a look at the designs on real boomerangs or didgeridoos for inspiration - do a quick Google image search.