Apologize to your little brother when you were wrong. You’re teaching him what strong people do.

Younger siblings learn how to handle being wrong by watching somebody older do it, long before anyone explains anything. If the older version never apologises, the lesson is that admitting fault belongs to people with less standing, and that is hard to unlearn later. Saying sorry downward is the only kind that teaches anything, because nothing is forcing you to.

Go and name the specific thing, without adding what he did first. Keep it to a sentence and do not require him to be gracious about it. He will remember how it was done far longer than what it was about.