My DD at 13 is old enough to recognize the benefit of producing commercial work. She also understands that some pieces are prepared to be sold and others to be treasured. With any luck, the two will be the same and she will have works that are both productions from the soul and also marketable. I know she wants to be self-supporting as an artist so we discuss how to make that happen. But, it is her choice. I encourage her by showing her examples of other artists who bridge the divide. (Book illustrators, people who sell prints and greeting cards, graphics design, etc.)
I foster her skills by letting her take online classes (live and video) from professionals. They have the talent to show her what she needs to know and give her tips and tricks. Plus, fellow artists speak and explain things in a way that she gets. They are her people. I know enough to recognize that her skills will need to be nurtured by someone well beyond my abilities as she matures. When the time comes, we'll seek those people out.
She used to show us all her art, now she keeps a sketchbook and only shows us those that meet her standards for display. She will practice the same line or idea over and over again. I don't say things like, "If you are going to be an artist you need to do X." (Which actually, since I'm not a successful artist or a professional art instructor or art historian- how would I know anyway? That would be like me giving a rodeo rider advice!)
I say, "I'm willing to purchase X (tool, equipment, lessons) for you if you are committed to using it." Watching art lessons or practicing then becomes part of her daily schoolwork. I do the same for my coder son. The child chooses whether to commit to the goal and then I help him or her achieve it.