I'm pretty sure everyone has made one of these with their kids, but just in case you haven't...
Garden stepping stones are super easy to make, and are actually a useful art project. (How many completely useless art projects do you have sitting on shelves in your house because you feel guilty for throwing them away?)
We've made them every year for the past few years, both footprints and hand prints. I finally have enough to line the flower bed in my front yard.
When I mix up the cement, I make sure to save enough to fill small containers for the girls to make their very own creations - random mosaics of stones, or whatever designs they choose. Those stepping stones go into their very own garden, adding a bit of beauty there too.
Michael's craft stores carry the supplies. If you use a 40% off coupon, it can be a pretty reasonably priced project. They also make nice gifts (since Mother's Day is around the corner.)
Is anyone else getting creative and decorating their garden space? I'd love to hear about your ideas!