Not to be a jerk (well maybe), but when I read this it makes me think of those who scream "we just new to enforce the gun laws we already have". Unless the son is giving dad a gun to so dad can murder somebody why is it illegal to give him the stinkin gun? For that matter, why is it anybody's business? Again, unless somebody's life is in danger leave it alone. Conditioned minds. There I said it!
x2. If you think there is a threat to someone's life, you might report THAT to the local Sheriff or PD -- but I'd leave the gun situation alone. As was already said, I wouldn't call the ATF on my worst enemy.