If the stadium is a group or component and they are editing it, they can set the rest of the model to disappear by ticking the boxes under Component Edit in Display.
They should also be learning how to correctly use layers. They can create a layer for the houses and another for the stadium and then control the visibility of those layers as they work.
Of course they can refine that so they might have the surrounding walls of the stdium on one layer and the seats on another and the playing field on yet another layer.
Remember to teach them that correct layer usage is important. Layer 0 remains active at all times.Pencil icon always displayed to the right of the Layer 0 name. All geometry is created on and remains on Layer 0. All geometry gets gathered into groups or components and only groups and components get other layer associations.