There should be more charges when these "accidents" happen. If owners can't keep the guns in safe places or away from idiots then they should be charged for irresponsible ownership or disregard of safety laws or aiding and abetting in whatever crime the gun was used or whatever...they should be punished in some legal way. Maybe it'll force responsible ownership.
And maybe there should be licensing just like with cars. With renewals every 5 years or so to make sure they remember responsible behavior, with safety tests etc. Just like the written and driving test for auto licenses...there should be the same sort of care with guns.