Give each child a sheet of waxed paper to paint on and tell them to fill the sheet up with color. They can do shapes, blotches, swirls... whatever. We used washable Crayola kids paints because they are my favorite and really are washable! Even my 3 year old got in on the fun! Just have the kids blot their paint brush on a dry paper towel between colors. No water needed. So clean!
While the paint is still wet, use the tip of your paint brush to add swirls and designs to your sheet. This was a really fun part for me. ;O) It's totally optional.
Once the paint is dry (which goes pretty quickly), cut each sheet of wax paper into smaller rectangles, ready for a frame. I already had some 4x6 frames from a previous project but you can just cut some from any color card stock. I had the kids decorate their frames with markers. Each child ended up with enough wax paper for two frames. I attached the waxed paper painting to the frame using Glue Dots, which I love. Now they're ready for the window!