“No-no; this is for grown-ups.”
You're drinking a beer. Your 3-year-old son is curious about it, so he asks if he can drink some.
No-no; this is for grown-ups.
When adults speak to very young children, they often say "no-no" instead of just "no". For example:
No-no! Don't touch that!
Celine! That's a no-no! Put the kitty down!
"Grown-ups" is a word that means "adults". "Grown-ups" is a word for children; children use it, and adults use it when speaking to young children.
Stryker, you do not go in the pool without a grown-up! Do you understand me?