My concern over a TLR isn't if it will break. It is if the hands of an eight year old could use it comfortably. Anyone have experience of a child using a TLR?
In some ways the TLR is easier to use than a folder.
The main issue for an eight year old with a TLR is the inverted image. It can be a little disconcerting seeing the image move the 'wrong' way when you're composing. The other bit that can be tricky is making sure you see the frame numbers properly in the window when winding on. It's easy to miss a frame if you can't see the tiny little numbers go by.
But other than that the Lubitel would be a good choice IMHO, as it's cheap, sturdy and far less delicate than a folder. It has the same style type of on-the-lens controls for aperture, shutter speed and shutter so would be a good intro to many other cameras with similar systems such as the Zeiss Ikons.
Don't tell anyone though, my most used MF camera is a Holga! It's a terrible camera in most respects, but I love the images and it's so easy to chuck into a backpack. My SQ-A only gets used for more serious photography, of which finding the time is very tricky. As part of a 'photo of the day' project, my Holga is probably my most used film camera and it's responsible for some of my favourite images. I've not used my 166 since I got the Holga (but am intending to fire it up again soon!).