Okay kiddo, do you know how sometimes you get sick and your body doesn't feel good? Well, invasion of the body snatchers is kind of like that, but even worse because something else takes over your whole body!
Picture this: you have a body with your heart, lungs, brain, and all your other organs that make you YOU. But one day, something called a pod falls from outer space and grows into a big plant. This plant creates a copy of you while you're sleeping, but it's not really YOU anymore.
The copy looks exactly like you and acts just like you, but it doesn't have any feelings or emotions. It's like a robot pretending to be human. And it wants everyone else to be like this too! So, it makes more and more copies of people while they're sleeping and takes over their bodies too.
These "pod people" want everyone to be the same with no emotions or individuality. They want to take over the world and make it a boring, emotionless place.
So, the invasion of the body snatchers is when these pod plants take over people's bodies and turn them into emotionless "pod people." It's a scary idea, but luckily it's just a story and not something that can really happen.