Okay kiddo, do you know what a bird is? It's an animal that has feathers, wings, and can usually fly up in the sky. But some birds are different, they don't have the ability to fly like other birds and they are called "flightless birds".
These birds come in all shapes and sizes, just like regular birds. But because they cannot fly, they have adapted to live on the ground. Flightless birds have strong legs that help them run quickly and they spend most of their time walking or running around.
Their body structures are also different from the flying birds. For example, their bodies are heavier and have smaller wings that are not strong enough to lift them off the ground. Flightless birds also have stronger bones to support their bodies on land.
One of the most famous flightless birds is the penguin. Penguins are really cool because they can swim very well but they can't fly. Another example of a flightless bird is the ostrich. Ostriches are really big and tall birds that can run up to 43 miles per hour.
So, kiddo, while most birds can fly, there are some birds that can't because they have adapted to living on the ground. They are called flightless birds and they are really fascinating.