For a certain gardening grandparent, I decided to make a stepping stone with each child's hand print on it. That means six of these suckers. Here's one in the process of drying.
I used a sack of quick drying concrete. Not the best choice because, though it's not real expensive (it was a little more than $5 for a 50 lb bag), it has lots of little rocks in it making it difficult to stamp the letters and numbers. But it works.
I mixed it in an empty plastic ice cream bucket. Just enough to do one at a time since it sets within 30 minutes. We poured it into the clear plastic flower pot dishes (surely there's a name for that) that we got at Home Depot for less than $1. They have similar things at Michaels near the stepping stone kits that sell for nearly $4. Not a good deal if you want to do 6 of them.
I DID buy the letter stamps at Michaels.
Something I might try sometime is buying patio paint and painting the handprints onto already made stepping stones.