Step 7: The mock x-ray machine and more about fluorescence
This is purely a trick, albeit one that children love. I normally draw a picture of a skeleton on the back of my hand using a yellow highlighter. This is only just visible in normal light, but glows strongly under UV, particularly in a darkened room. If you are really up for some mess, give the children some highlighter pens to play with!
You can do some further explorations into UV by looking at normal copier paper and white clothing. Copier paper and washing powders both have fluorescent substances added to make them glow slightly and appear 'whiter than white' when there is UV present (as there is outdoors). This knowledge can be used to extend investigations into the comparison of washing powders to see if they are really cleaning the best, or are getting a helping hand by using fluorescence.