These are web links for websites that can be used in an Elementary Art Class. The First 3 I found and described and the rest come from the 2011 summer staff for Jefferson Elementary Community Ed.
Incredibleart.org---Elementary Art Lessons
Some of these are for more experienced art students but there are some useful lessons such as Trash Collage that can be used for any age or ability level.
Really good source for origami. Has instructions in both diagram and animation form. Has super easy origami for Kindergarten age up to harder variations for older students. Website is very well organized.