High winds blew packaging material from a nearby building site all around our town. The pieces of polystyrene got lodged in trees, shrubbery, everywhere. They were too big to put in the bin for collection so we decided to make them into something pretty after school.
UPDATE - We have since made another one of these using florists ribbon (or you could use cassette tape) to make a waterproof, outdoors version.
Step 1: Get your polystyrene
We chose this particular piece of polystyrene because it was large enough to be worked on by several little people at once and the little people liked the shape.
The polystyrene is several inches thick so pieces won't break off easily (although lots of tiny particles will make a break for freedom so you might want to do this outside when it's not windy put a sheet down etc).
Mum removed the branches and twigs embedded in the polystyrene from where it got blown into bushes.