About 554 children in the US under the age of 12 have been killed by firearms since December 14, 2012, the day that Adam Lanza stormed Sandy Hook Elementary School and killed 20 children, an NBC News analysis showed.

While the Sandy Hook Elementary School massacre was considered as the worst involving children under the age of 12, the NBC report said the school killing was nothing compared to the 554 American kids that have died from gun-related incidents since then.

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The figures released by NBC were based on several research and sources, including The Gun Violence Archive, GunDeaths Twitter feed, and Slate.com. The information gathered were then fact checked by the NBC News team.

The numbers seemed to underscore the gruesome fact that American children have an increased risk of dying by gunfire since the Sandy Hook incident.

The report, which was released by NBC News on the anniversary of the Sandy Hook Elementary School shooting, showed that mass shootings still account for a tiny portion of gun deaths involving US children.

According to NBC, while mass shootings often get the attention of major media organizations, it is the steady deaths in ones or twos, in homicides and suicides, even in gun-related accidents, that account for the majority of the 554 deaths of children.

Data released by the Centers for Disease Control and Prevention (CDC), which looks at death certificates to determine cause, showed that the number of gun-related deaths involving American children 14 years and under reached 6,495 from 1999 through 2014.

Homicide was seen as the leading case of death by gun for kids and young teens, followed by suicide and unintentional, according to the CDC data.

Last year saw the highest number of cases of gun-related deaths in American children and young teens, at 460.

By gun type, handgun - pistol, revolver, etc. - was the leading gun of choice, followed by rifle, shotgun, and others, according to the Federal Bureau of Investigation's Homicide Report that covered from 1980 through 2013.

TagsSandy Hook, Sandy Hook Elementary School, Sandy Hook Elementary School Shooting, US School Shooting, US Children Deaths, Deaths of US Children, School Shooting in the US