Whether you are looking for an art lesson to supplement your studies, or you are looking for art projects to keep your middle schoolers busy during vacation, a great resource for art ideas for middle schoolers is the Incredible Art Department website by Princeton University.
This site must have between 200-300 art lessons on a whole variety of artists, time periods, topics, and themes, as well as utilizing a number of different art media. It is searchable by such things as artist or time period, and includes other resources (such as PowerPoint presentations or outside books) that will help the teacher.
So if you are looking for an art project, go check it out. It is one of my "go-to" places for art ideas.