Apologizing to your little sibling teaches them more about being a good person than any lecture.

Children learn conduct by watching what adults and older siblings actually do under pressure. An apology from someone with more power in the room demonstrates what no explanation can: that being wrong is survivable, and that standing does not exempt you from repair. They will remember the behavior long after forgetting every instruction.

If you snapped at a younger person recently, go back and name it specifically without adding a justification. Say what you did and that it was not fair. It will feel disproportionate for such a small thing, and it is the part they will copy.