Hey kiddo, have you ever heard of science? It's this thing that helps us understand how things work in the world around us. Sometimes, scientists come up with ideas, or theories, and they test them to see if they're true.
Now, some theories turn out to be wrong, or not completely right. When this happens, scientists come up with new ideas that explain things better. And these new ideas replace the old ones. That's what happens when a theory is superseded.
Think of it like when you learn something new in school. Maybe you thought 1+1=2, but then you learn that sometimes 1+1 can equal 3 or 4. You wouldn't use the old idea anymore, because the new idea is better and more accurate.
It's the same with science. The old theories are replaced when new and better ideas come along. This is what makes science so cool – we're always learning and improving our understanding of the world!