My favorite moment with a kid that age was when I told my nephew he wasn't allowed to go into an ornamental fish pond and he, after considering my instructions for a moment, asked me "What about if I accidentally fell in?".

Meaning that they're often very good at figuring out how to interpret the rules in a way that works best for them, and not yet very good at figuring out how to foresee how others will view their actions. So while teaching little kids that they are allowed to defend themselves is a very important lesson, it's hard to get them to appreciate nuance. Nuance is tricky.