There's many studies, and it took me two minutes to find this one:
Gun "accidents" are not necessarily the biggest risk from these family-owned guns, say the researchers.
In 1998, 55 percent of gun deaths among children aged 10 to 18 in North Carolina were homicides. Thirty-nine percent were suicides.
"In North Carolina, the majority of gun deaths among [kids] are … suicides," says Coyne-Beasley. "Most teens … who commit suicide do it with a gun they find in the home.
"If [the gun] is locked up, unloaded, and the ammunition [is] locked and stored separately, [it provides] a cooling-off period before they can hurt themselves."
The study looked at 286 parents visiting hospital emergency rooms in North Carolina. Ninety-four owned guns and had children under the age of 7. --
http://abcnews.go.com/Health/story?id=117480&page=1
and this took another 5 minutes to find:
Having a gun in the home is associated with an increased risk of firearm homicide and firearm suicide, regardless of storage practice, type of gun, or number of guns in the home.1 Guns kept in the home are more likely to be involved in a fatal or nonfatal unintentional shooting, criminal assault or suicide attempt than to be used to injure or kill in self-defense.2 Rather than conferring protection, guns in the home are associated with an increased risk of homicide by a family member or intimate acquaintance.
Research published in the New England Journal of Medicine found that living in a home where there are guns increased risk of homicide by 40 to 170% and the risk of suicide by 90 to 460%... --
http://smartgunlaws.org/guns-in-the-homesafe-storage-statistics/
and this:
Data from a US mortality follow-back survey were analyzed to determine whether having a firearm in the home increases the risk of a violent death in the home and whether risk varies by storage practice, type of gun, or number of guns in the home. Those persons with guns in the home were at greater risk than those without guns in the home of dying from a homicide in the home (adjusted odds ratio = 1.9, 95% confidence interval: 1.1, 3.4). They were also at greater risk of dying from a firearm homicide, but risk varied by age and whether the person was living with others at the time of death. The risk of dying from a suicide in the home was greater for males in homes with guns than for males without guns in the home (adjusted odds ratio = 10.4, 95% confidence interval: 5.8, 18.9). Persons with guns in the home were also more likely to have died from suicide committed with a firearm than from one committed by using a different method (adjusted odds ratio = 31.1, 95% confidence interval: 19.5, 49.6). Results show that regardless of storage practice, type of gun, or number of firearms in the home, having a gun in the home was associated with an increased risk of firearm homicide and firearm suicide in the home. --
http://aje.oxfordjournals.org/content/160/10/929.full
And there's plenty more where these come from.
BTW, I mentioned it before but I'll briefly mention it again, namely that even though anthropology was my main subject to teach, the other one was political science, which I taught for around 25 years. Every semester I brought in law enforcement from the state or local police or the FBI or the Border Patrol, and every time I or a student asked them about having a loaded gun in the house, the answer was always the same:
no.