When they see the finished product, they will want to do it. Most artists are not happy with just one medium.
Hang in there!
Do you do this for a living?
One of the twins (the girl iteration) is actually something of an artist herself and wanted to see the process. I'm a mentor/cheerleader for her art. Since she mainly does pencil art, it's a medium that she could adapt to easily.
I'm betting she would make her brother do the dangerous chemicals part of the process though...
/johnny