Wanted to share a neat web-site my daughter and I use from time to time. There are free drawing lessons available to you and your children! You also have several options to take classes for a fee if you wish (we have not).
Visit Drawspace to see the levels of drawing instruction provided. I think your 7th grader and up would do very well with these lessons.
*Please pre-view the many galleries of member drawings before you let your child look through them. Occasionally you could find something objectionable in a gallery so I encourage you to either disregard this feature or use with discretion.