Ah good catch, they must have rearranged this when they added Stage Manager. It's more obvious now with its own "Multitasking & Gestures" in the top level settings categories, right above Accessibility.
There are three choices now: Off, Split View & Slide Over, or Stage Manager.
The real trick with Settings though is that it has a search bar at the top of the sidebar (with no visual indication that it exists unless you find it by scrolling up past the top), so you can always use that instead of hunting through the many pages of settings.
Parent commenter should probably turn off the 4-finger app switching gesture and the 3-finger undo/redo/copy/paste gestures as well. Doesn't seem like a feature their mom will be learning to use on purpose.
