Original sentence: I hide my nest in the grass and rarely fly.
Is it correct? Yes — it is grammatically correct. The subject "I" applies to both verbs (hide and fly), so the sentence is fine.
Clearer alternatives:
- I hide my nest in the grass, and I rarely fly.
- I hide my nest in the grass. I rarely fly.
Simple explanation for a 7-year-old: The sentence is okay. It means the same as saying two short sentences: "I hide my nest in the grass. I rarely fly." Adding "I" before "rarely" makes it a little clearer, but you don’t have to.