Your original sentence is mostly clear but can be improved slightly for smoother reading. Here is the corrected version:
Original: All animals need to eat so they can have energy to move and grow. Some animals can be food for others.
Corrected: All animals need to eat so they have energy to move and grow. Some animals can be food for other animals.
Explanation:
- We changed "so they can have energy" to "so they have energy" for simpler flow.
- Added "other animals" instead of just "others" to be clear that animals are food for other animals.
This version is easier for a 7-year-old to understand and grammatically correct.