We just rolled out the clay on waxed paper on a flat tray and I took Ollie's hand print, then cut out a circle around it. Then I used a little water on my fingertips to smooth out any cracks around the edges. I like this air dry clay better than the FIMO baking clay - smoothing cracks out with water is very convenient. I also like it more because it's much softer - easier to mold and easier to make hand prints with. It's also so much cheaper - you can get a big tub of it for $5 on Amazon. The only downside is that you have to wait a few days for things to dry completely before you can paint them. The directions said 24-48 hours, but I found that it was really more like 3-4 days - and that's in a house with dry winter air with very low humidity. So it definitely requires some patience in between.
Once the hand print finally dried, I painted it with acrylic craft paint in contrasting colors to make the print really stand out.
Oliver also made some sculptures that dried and we're going to paint them. He loves painting. And the tub of clay is big enough that we'll have enough for at least two more crafting sessions... and then I'll probably just order more because he's having so much fun!