Okay, imagine you are standing on a really big ball, like a super giant bouncy ball. Pretend you're tiny, like the size of an ant. Now, when you look around you, do you see a big curve all around you? That's because the Earth is like a giant ball too, but way, way bigger than the one you're on. It's so big that when you look at it from far away, it looks flat, like a piece of paper. But when you look closer, you'll see that it's actually round like a ball.
Let's think of the Earth's shape like a pizza. When you have a pizza, it's round, right? Well, Earth is also round like a pizza, but much, much bigger. So, even though it may look flat when you're walking around, it's actually round like a ball when you see it from space.
Now, imagine you have a really big magnifying glass that can make you see things very far away. If you look at the ocean, you'll notice that ships disappear slowly as they sail away from you. That's because the Earth is curved, and the ship is going over the curve as it moves further away from you.
One more thing to remember is that when you look up at the sky, you can see the moon. And guess what? The moon is round too! Just like the Earth. So, since the moon is round, and we can see it from the Earth, we know that our planet is also round.
So, even though it may seem like the Earth is flat when we're walking on it, it's actually a big round ball floating in space. Just like how some toys might look one way up close and different far away, the Earth's true shape is round when you look at it from far away.