I started a new class this fall that is specially designed for two and three year olds. It is process based and many of the classes to do not culminate in a take-home product, and the lessons often involve collaboration.
This painting lesson was the first class, and is from Meri Cherry so click over to read her post. I asked the children not to mix the paint colors for the first half of class, and towards the end I invited them to start mixing, which held their interest. I also brought out sponge brushes towards the end of class. Painting on plastic is pretty fun- the paint really glides across the surface and it feels different than paper. I painted a blue outline around the plastic, and I also taped larger paper behind it to keep the walls clean. Also, this is a secret: I just used trash bags!