Great idea! Used at a children's spy party. The kids loved them, I bet some markers didn't show what was written in invisible ink. I'm not sure if the problem is with the pen or marker. I've tried all the problematic pens myself to make sure it's not just kids who write sloppily, but they still don't work.
Rainbow Spectrum Secret Viewfinder
7 Review
π΅οΈ Exclusively on Amazon: Uncover the Hidden Enigma Mission
6 Review
SCStyle Invisible Ink Pen Set Of 10 With UV Light - Magic Spy Marker For Kids' Secret Messages, Party Favors, Easter, Halloween, And Christmas Gifts
15 Review
π© Invisible Birthday Halloween Christmas: Unveil the Magic with VOVRU
7 Review