Like many mid-20th century parents, they simply use the web browser and basic office suite. They aren't likely to do something unstable, and (if my assumptions are correct,) even if they encounter an error, they're likely just to hit the 'X' or 'OK' and move on, not thinking anything of it. That's the irony of it. Linux distributions are perfect for "clueless" users if set up right, but to set it up right, you need someone who isn't clueless. A little less than the opposite, in fact.