Here’s a clear, kid-friendly way to say the idea with good grammar:
Original: Baby oryx horns start short and get longer as they grow.
Corrected version: Baby oryx horns start short and get longer as they grow up.
Why this works:
- Use grow up to talk about getting older in a natural way for kids.
- The verb start and get describe a change over time, which fits the sentence well.
Alternative simple version: Baby oryx horns are short at first and grow longer as they grow up.
Both sentences are clear, correct, and easy for a 6-year-old to understand.