Here is a fun project that would be fairly simple for anyone to do at home, and kids can help. This came from Creative Concrete Ornaments for the Garden by Sherri Warner Hunter, though the mushrooms in the book are far more finished looking than our first attempt. They are still cute.
First, we filled some plastic storage bins with sand. Any large containers will work for this. Then we made indentations in the general shape of mushroom tops, inverted. Anouk placed glass gems and bottle tops in the sand for decoration.