I recently visited my child's elementary school to speak to a science classroom about rocks and minerals. While trying to explain what a crystal is, I got sloppy and mis-spoke that an atom was the smallest possible piece of matter (rather than an element!) I was quickly stopped and corrected by a 9-year-old that told me in fact atoms can be split into leptons and baryons. I told her she was right, and explained that if an atom of an element is divided it becomes a different element (overlooking isotopes!).
My knowledge of particle physics is limited and later I began wonder what I might be leaving out, that should not be left out, when talking of the types of 'ordinary matter' in nature. What happens in high-energy physics experiments aside. I know that there are other elementary particles besides leptons and baryons, photons are obviously everywhere.
But if we restrict the discussion to radioactive decay, fusion in stars, cosmic rays, is everything a lepton, baryon, or a photon?