Here are three simple rephrasings for a 7-year-old:
- Our Earth is the only planet with living things. Tiny bugs and huge whales are both happy to live here.
- Earth is the only planet where life exists. Little bugs and big whales enjoy living here.
- No other planet has life like Earth does. Small bugs and giant whales all live here happily.
Each sentence keeps the same meaning but uses different words.