You will need:
Exacto Knife/Razor Blade
Brown marker (optional)
An adult needs to prepare the stamp in advance by cutting 2 nicks at the opposite sides of the same end of the cork (doesn't make sense? Check the photos below). Now provide the kids with the paint, paper and corks and show them how to "press and lift"- Press the cork in to the pint and lift, press the cork onto the paper and lift.
You can use the brown marker once the paint is dry to draw stems. I like to use this technique on the cover of my cards and then place a photo of the kids in their apple costumes inside the card.