9 years old is probably old enough to understand the truth- he was mentally ill and left home.
Grandparents are in denial. Wonder if they ignored the signs of mental illness as well, which only serves to compound the problem.
My IL threw their mentally ill son out on the street because he kept getting into trouble. To be fair, back then (30+ years ago), the general population didn't understand mental illness or how to treat it. Even in present times, people think it's the devil and prayer is the only solution
