Ten-year-olds understand quite a lot of things. They don't always think before they act, but they would absolutely understand this object lesson.

It's water. It's not harmful. Getting splashed with water is most ten-year-olds' idea of a good time in most scenarios.

Is this the most constructive way to go about teaching a kid how to behave properly? No.

Is this going to scar the average kid for life? Also no.