This is an activity for older children who can write, or at least dictate to you what they want to write. I got this idea out of a parenting magazine and have always wanted to try it. They called it art, I don't know about that, but it still seemed fun.
Turn a tree in your yard into a wish tree. Put up a sign that reads "Wish Tree" and some directions of what to do. Somewhere by the tree and sign put a container with your "supplies". All you need is some scrap paper, a writing utensil and string. The idea is for people to write down a wish and hang it in the tree. You probably want your family to write down some wishes and hang them in the tree first so that people get the idea.
This would also work really well as a Thankful Tree, Why I Love America Tree, etc. depending on the time of year and what you want your family to think about.
Don't have a tree you can use? You can draw one and hang it somewhere inside your house, or use some sort of necklace hanger, or even bring a few branches of a tree inside your house and set them up. Have fun seeing what your kids or neighbors are wishing for!