This is an issue of responsibility.
Children cannot legally buy or own guns until they are at least 18 years of age, to the best of my knowledge.
I know some gun owners train their kids how to safely handle firearms,and in some parts of the country (mostly rural areas) the culture surrounding guns is totally different than it is in others.
I know folks who take their kids hunting and trust them fully with their firearms, which is absolutely fantastic.
However, the fact remains that adults are responsible for their firearms and IMHO, should be held accountable for their failure to secure them.
Losing a child is a horrible event.
My sister lost her 9 year old son two weeks before his 10th birthday to cancer many years ago and she still isn't over it and I believe if it had been due to something that was preventable it would have been even harder for her to cope with.