I have seen this done with painted pasta, but straws come pre-coloured, perfect for lazy Mums like me! I took a load of straws (£1 for a gazillion) and chopped them up in to various sizes. I also cut varying lengths of string for them to thread the straws on to. I did have to wrap a bit of sellotape around the ends to stop them fraying.
I did discover that the straws were ever so slightly frustrating for George, so I cut some extra thick straws up for him too. And Hannah loves her stylish new necklace!