I agree with Aniseteph, the child should not be allowed to be disruptive and the mother should control her child, it also wouldn't hurt the instructor to step in and say something to the boy, often children will listen more to someone other than mum.
On rare occasions we have had a child come with Mum to a class because of some unplanned circumstance, and the children have been wonderful, sitting quietly watching or reading/playing nintendo on a hand held etc. They have never been an issue.
I know if it was me, I would actually speak to the child myself, and quietly but firmly ask/tell him to be quiet..... but I am probably a lot older than you, and it is easier to do that when ones kids are grown or you have grandchildren
One gets a bit "bossy" in their autumn years LOL! When I was in my 20s/30s, I doubt I'd have had the courage to do so.
Your instructor should be taking charge period!
~Mosaic