I haven't met one yet. These pens will be a hit with any child who can write and who enjoys making up their own games. It's the simplest thing but it really is fun. These would be a treat for kids who like secret spy games, crime-solving or super-hero games, for those who like passing secret notes or leaving clues that only certain people can see. Write notes with these pens and the words disappear almost immediately. But there is a special UV light at the other end of these pens. Anyone who has one of these can shine that light on the page where the invisible message was written and - voilà! - the message appears! I think these would make brilliant party favors or Valentines Day gifts. I'll bet teachers could find lots of ways to use them in the classroom and they'd also make terrific end-of-the-school-year gifts to encourage kids to practice handwriting and spelling over the summer