This is a great craft to do with elementary-aged kids, and is do-able for littles. I did resort to gluing the stencil on the pots so that my two year old wouldn't accidentally paint underneath, but the glue came off well enough (but, my fingernails were too long anyway, so... yeah.)
The children and I made two pots for their grandmothers for Mother's Day. One is green and the other is yellow. I wanted to buy one green and one red, but Walmart didn't have any red glazed clay pots, so we went with yellow instead. You'll notice that the yellow pot seems to change colors throughout this tutorial. I was having a hard time photographing it, both with and without flash.
You'll also need a foam paintbrush, acrylic paint in the color of your choice, clear sealing spray, and a picture.
I used a drawing of tulips that I found online. After printing the picture in the size I wanted, I cut out the interior to make a stencil.
Lay the stencil on your pot and tape down. If you're working with toddlers or young preschoolers, you might want to consider gluing it down. I used hot glue, which worked okay. We had some bleeding edges and I had to pick all that dang glue off when we were done, but it served the purpose. The stencil didn't move an inch! If you go with hot glue, make sure to stick it down in sections, so that the glue smooshes onto the pot and the edges are pressed down nicely. This will make it harder to remove, but the end product will look better.
Use your foam brush and acrylic paint to paint the inside of the stencil. I did 3 light coats. Make sure the paint is all the way dry in between coats, or the wet paint will rub off when you try to paint over it. Also, don't put it on too thickly, lest it peels. After you're all done painting, let the pot dry for 24 hours.
Then, remove the stencil.
If you glued the stencil down, this is what you'll get. Next, you'll have to pick and scrape off all the glue. I found that a nylon pan scraper worked best for this. Be careful not to scrape over the flowers, or even touch them too much, because the acrylic paint will still peel off at this point.
After you have scraped off all the glue, you'll be left with something like this. This is caused by the paint bleeding under the edges of the paper. Obviously, if a grown-up is doing this, instead of a child, your bleeding won't be as extensive. To clean it up, take a toothpick, dip it in some water, and start scratching the excess paint away. Also use the toothpick to clean up the edges of your flowers.
You may still have a residue of paint specks and glue when you are finished with the toothpick. In that case, use a small, damp paintbrush to clean up your pot.
After you're done cleaning up your speckles, take a new dampened toothpick and scratch some detail into your flower petals and leaves.
When you're satisfied, go outside and spray your pot with clear coat.
You'll want to do two to three light coats to make sure the acrylic is sealed well.
Put a plant in there and display or give it to someone else. I'm torn between planting a flower in each pot or some herbs. I figure the flower will be more colorful, but the herbs will be more useful. Regardless, I'm sure the grandmothers will love them, flaws and all.