The following video shows the kinds of microscopes and the advances they enabled: https://www.youtube.com/watch?v=6vZZeWqbmU8
Viruses are too small to be seen under a light microscope. They were first seen under the electron microscope developed in the 1930s. Type into your browser: viruses electron microscope images
This opened up a hole new area of biology: virology
Advances in microscopy continue. Quite recently (2017) a new kind of microscope was developed—the “merging lattice light sheet microscope” described here:
https://www.hhmi.org/news/new-microscope-captures-detailed-3-d-movies-cells-deep-within-living-systems
Some of your kids may be using this microscope to make new discoveries.