Imagine there's a really cool toy that only a few kids have. But the problem is, those kids are starting to get older and don't want to play with the toy anymore. That means, if no one else starts playing with the toy, it might get forgotten and everyone will miss out on all the fun.
A similar thing can happen with languages. Some languages are spoken by only a few people, and if those people stop teaching it to their children, the language might disappear completely. When a language is in danger of disappearing, we call it an endangered language.
Languages become endangered for lots of reasons. Sometimes, people feel like they need to learn a different language to get a job or make friends. Sometimes, governments try to force people to speak a certain language instead of their own. And sometimes, bad things happen like war or disease, and people who speak a certain language have to move away or die.
When an endangered language dies out, it's like a little piece of human history and culture disappears too. That's why it's important to try to keep endangered languages alive. People can do this by teaching their children the language, documenting it in books and recordings, and even having special events and celebrations to keep the language alive.