Where to get child's art made into reverse painted Christmas ornaments?

I found 3 christmas ornaments made in reverse painting style at a thrift store. At first I thought they were made by adults to look like a child's art, but after careful examination I realized that wasn't the case. It appears that someone took their child's artwork and sent it in to be made into an ornament, somewhere. The ornaments are round of really thick gl with the paint on the inside...Is there a specialty store that these could have been made at? Somewhere online maybe? Does anyone know?