Okay kiddo, so you know how there are some really big and really powerful weapons called nuclear weapons that can cause a lot of damage and harm to people and the environment? Well, a bunch of countries got together and made a special agreement called the Treaty on the Non-Proliferation of Nuclear Weapons.
This treaty basically says that some countries, called the "nuclear-weapons states" (like the United States, Russia, and China), are allowed to have nuclear weapons. But other countries, called "non-nuclear-weapons states," are not allowed to have them.
The treaty also says that the nuclear-weapons states need to work towards getting rid of their nuclear weapons, and the non-nuclear-weapons states need to promise not to develop or acquire them in the future.
The treaty has been around for over 50 years now, and it has helped prevent the spread of nuclear weapons to other countries. It's kind of like a big promise that all these countries are making to keep everyone safe and make sure that nuclear weapons don't become a bigger problem than they already are.