This is one of my favorite activity for Guides Own. It fits in well with themes like Summer, Wild Flowers or even Water.
Before Guides Own each girl need to colour a flower with crayons. They should be encouraged to make their flower unique. Then the petals of the flower are each folded in to the middle. Bring a shallow basin (even a cookie sheet can do) filled with water to the Guides Own. When you are ready, have each girl float her flower on the water and the petals will open.
You can find template for magic flowers here.
This video shows the technique but they use pre-coloured flowers.