The sentence you wrote is almost perfect! Here's a corrected version for better grammar and clarity:
"Corals look like plants, but they are tiny animals with a mouth and tentacle-like arms."
Explanation:
- The sentence is clear and easy to understand.
- Adding a comma after "plants" helps separate the ideas.
- "Tentacle-like arms" is a good description for the tentacles of corals.
So your original sentence is grammatically correct and well-written for a 7-year-old to understand!