I found this really fun lesson on
Art with Mrs. Smith. (I had to adapt it a bit to make it work with third graders, but the idea is mostly the same). This lesson was inspired after Frida Khalo's
Still Life with Parrot and Fruit.
For this lesson, I wanted to focus on analogous colors and color blending. We used oil pastels for this lesson, which is wonderful for blending colors. When drawing the fruit, I asked the students to use three colors. I had them first choose the main color for their fruit, and then its analogous color. For example, if they were coloring an orange, they would use orange, yellow, and red. I then asked them to blend these colors together by smearing with their finger.
After the fruit was drawn, I had them cut the fruit out and lay it onto their paper. I encouraged them to overlap some of the fruit, to make it look like one was in front of the others. After gluing these to their papers, I had them use a black pastel to create a small shadow under the fruit.
I found this really cool artist online recently. Her name is Margarate Godfrey, click on the link to see her blog. I used this artist as inspiration for a volcano lesson with my fifth graders. Here is what my fifth graders created.
For the volcano, we used scraps of construction paper and tissue paper. These were collaged and glued to the paper. The lava was made with liquid water colors. We used a straw to blow the liquid watercolors. This made the liquid watercolors spread in random directions, which looked more like real lava. The sky was then painted with blue and purple watercolor paints. 
