First off, one question I got was what is the target age of Sowing While You Sew? My answer is you know the child the best, but I would say from 8-12 (or older if they're interested). You could start a little younger if you think they are ready and can follow instructions well.
Second, how to do the basic stitch. Here are my very simplified pictures to hopefully help.
Imagine the line and points are labeled with the A, B Cs. The black line is where you want your finished stitched line to be.
First, you come up at point A, making sure to pull the knot up all of the way.
Next you go down through point B, making a neat stitch from A to B.
After that you come up through point C, again pulling it all the way through.
Next you are going to go down through the same hole as before at point B, making a neat stitch from point B to C.
You continue on to point D, making sure to pull the thread all of the way through.
Next, you go down at point C, through the same hole as before.
Continue up through point E, pulling the thread all the way through.
Then you back down through point D, making a stitch from point D to point E.
And you just continue this till you get to the end and tie it off underneath. For curved lines, you'll want to make smaller stitches in order to get the rounded effect. If you run out of thread before you get to the end, say after you go through point D. You would just come up at point F, pulling until your knot is caught, and then go through point E, continuing on as before.
Hope that makes sense!
Finally, a question about the pen. It's just a water soluble marking pen I get at JoAnn's on the notion wall. I use mine for a lot of things besides drawing designs and find them very handy.