Clothespins...use washi tape or glue paper on. Buy clothespins in the laundry section, not crafts. They cost about $.02 each. Even with washi tape, these only cost pennies to make. For $6 you could cover 100 clothespins and buy a couple rolls of fun tape.
Clothespins on frames. Easy to change out new artwork from the kids. I am pinning this because I really like the caulk board frame, and I love the different sizes and colors, but I think I would go with a cork board back instead of clothes pins.