Start by cutting a shamrock shape out of green card, I did mine freehand but you can also grab our free shamrock template to make this a bit easier. I also recommend using card rather than paper for this craft as it will hold a lot more paint before it goes soggy.
Scrunch your kitchen foil up to make a shape that you can dab into the paint and paint with.
On the plate place your green, blue and yellow paints. You can encourage your child to make green paint themselves by mixing them, using a plate means that the paint is a lot easier to access (and less likely to get knocked over) than if you pop it into a pot. Using just the green paint is easier but it's fun to look at what different shades of green you can create with a bit of mixing.
Dab the paint all over your shamrock shape using your foil until it is covered.