All you need are some foam sheets that you will pre-cut into shapes. These don't have to be perfect or even actual shapes. Here is an example of my handiwork.
Then just fill a cup with water and supply a paintbrush. You can do this activity outdoors or indoors so it makes for a good rainy day or "too hot out" activity. You will also need a window. If you don't have one at your child's level I imagine this would work just fine on a mirror.
I showed the girls how they could "paint" the back of the shape with water and then "magically" stick the shape to the window. They loved how the pieces stuck up there. I kept this very open ended at first, but was surprised when the girls started combining the shapes to make things. B was the first. She was super excited that she made an ice cream cone using a triangle and a circle. "A" made a house by using a larger square and a triangle. I think next time I may make a few more shapes keeping in mind what they can build with them.
Probably my favorite part of the activity was the fact that lil' C could participate as well. She puts absolutely everything in her mouth which prevents her from doing a lot of activities with us, but she had fun with this. I think most of her fun was had because she did the same thing her big sisters were doing. C is 20 months old and I think this activity will work for her age or younger.
Nothing like sisters working together.
There is so much you can do with this activity depending on the age of your child. You can use it to review colors, shapes, cut the foam into letters and have your older child spell words, etc...I am sure you will come up with your own creative spin on this. The best part? When you are done, the foam pieces can be put away and used again so your $1 investment is going to last you a good, long time. Oh and you might be able to trick your child into cleaning your windows. I was not.