don't be alarmed. eardrums often spontaneously rupture and cause a little bleeding so this is the most likely reason for the dried blood. this is really nature's way of dealing with an infection and/or increased middle ear pressure. the eardrum quickly heals in the vast majority of cases and most middle ear infections resolve spontaneously. it is rare for ruptured eardrum to result in any long-term problems like deafness. i suspect there is more to the story with the grandparents than just a ruptured eardrum. the grandparents lived in a time where there were few if any antibiotics and medical care may have been sparse. since you are concerned it would be best to have your son examined by his medical provider.
my 5 yr old woke up with dried blood in her ear. she had an earache 2 days ago i gave her ibuprofen. no ear pain since. her grandmother and grandfather both became deaf at a young age due to their eardrums bursting. could this be serious?