Some of the lessons I learned as a child:
If you give your favorite dolly a haircut, a really short, crappy haircut, IT WILL NOT GROW BACK. EVER.
Sugar is NOT the opposite of salt. If you over-salt something, adding sugar will not cancel it out. Or make it better.
Snake poop REALLY stinks. This is why you should never carry a snake in your pocket.
You can’t buy a 10-cent Fudgsicle® from the ice-cream truck with ten thousand dollars of Monopoly money.
Take your retainer out BEFORE you go up to the front of the class to give your oral report.
Just because something is labeled NON TOXIC, that doesn't mean it's actually EDIBLE.