Mix cement and water in a large bucket with a trowel. Continue to add water to the powdered cement until you have a mixture that is similar to cake or brownie batter. You don't want it to be so thick that you can't stir it, but making it too watery will create a poor handprint.
Pour the cement mixture into a plant saucer or stepping stone mold. Smooth the top of it with a stiff spatula or old gift card. Work quickly before the cement begins to harden.
Dip your child's hand in the oil. Instruct him to spread his fingers out completely to get a good impression and press his hand or hands into the mold. If you don't get a good impression the first time, smooth the concrete out and repeat the process.
Add gems, decorative stones or words to the mold to make it more personal.
Remove the stone from the saucer after several days. Wait until the cement is completely dry.