As a high-res monitor user, with proper mouse acceleration it's really not any harder to hit a menu item that is anchored to the top of the screen than it is to stop the mouse on a menu item 200px away.
The only issues I've seen are when I have a non-rectangular monitor configuration.
Proper mouse acceleration is a poor poor solution for the parents problem. I can't (physically can't) use a mouse that moves faster than a certain speed.
The only issues I've seen are when I have a non-rectangular monitor configuration.