Here are three simple ways to say that sentence for a 6-year-old:
- Our Earth is the only planet that has living things. Tiny bugs and big whales both live here and are happy.
- No other planet has life like Earth does. Little bugs and huge whales are both glad to live on Earth.
- Earth is the only planet where animals and plants can live. From tiny bugs to giant whales, they all live here and are happy.
Why these work: each version uses easy words a 6-year-old knows, and each one shows that both very small and very big animals live on Earth and feel happy there.