May you explain radioactive dating to a 10 year old?

All organic material (anything that contains carbon, like plants, rocks, fossils, people, animals, etc.) has isomers of carbon that are radioactive. As the measured isomer (generally carbon 14) radioactively decays, there is less and less of it. It decays on a very precise time line that can be used to calculate the amount of time that the individual has been decaying carbon-14, aka the time that it's been dead. Based on that, you can guestimate, to a fairly accurate degree, the age of the material. Hope that's simplified enough for you!