We did a patio outside once. The idea was to make paving stones with designs to commemorate events, people, or places.

There are several types of paving stones you can make.

The first type is a negative stone. You get some wet play sand in plastic boxes. Make designs in the sand and pour an inch or two of mortar into the boxes. When the concrete dries pop the blocks out and use them to pave an area in the garden. You have to remember with these that anything you push into the sand sticks out on the final block. If you are going to write words they have to be backwards so when the block is flipped over they can be read. Those little magnetic fridge letters work great.

Another type of stone is made by pouring concrete into a plastic box and pressing things into the surface. If you want to remove the things you press in make sure they are smooth and don't have any under hanging edges that will get trapped when the mortar sets. You can also do the Grauman's Chinese Theater type blocks with hand and foot prints. A little lotion on your hands will help because concrete is alkali and can dry them out.

A third type of stone you press things into the surface and leave them there. Put keys or other metal knickknacks, seashells, colored pebbles. One woman made a mosaic using her grandma's Wedgwood plate that had broken years earlier. Some people use colored glass from bottles.

You could turn this project into two or three sessions. Have one where you set up the things to put into the paving stones. Have another session where you make the stones, have another where you set up the patio in the garden.