Alright kiddo, have you ever seen those little tags on your clothes that tell you what size they are and how to wash them? A taggant is kind of like that, but it goes on things like pills or money instead of clothes.
Taggants are really small particles that have special information in them. The particles are usually made of something safe, like plastic or metal. The information they hold can be things like when and where the product was made, or how to make sure it's not a fake.
Let's use medicine as an example. Sometimes bad people make fake medicine and sell it to people. This can be really dangerous because the fake medicine might not actually help the person who is taking it. To make sure that the medicine is real, the company that makes it can put taggants in the pills. Then, when someone buys the medicine, they can use a special machine to check the taggants and make sure the medicine is real and safe to take.
So taggants are just little particles with special information in them that can be used to make sure things are real and safe. Cool, huh?