The Invisible Ink Pens by Daemson are a set of 7 marker pens that can be used for secret writing. These pens require 3 LR44 batteries (included) to function and are recommended for children aged 3 years and above. The upgraded spy pen in this pack includes a UV light for revealing the hidden ink, making it a fun and interactive tool for young writers. With its multicolored pens and unique features, this product is sure to provide hours of entertainment and creativity for kids.