There are thousands of children killed every year at the hands of adults. It is VERY unfortunate and there's little we can do to stop it. Often the warning signs are not there until the crime is ultimately committed.
So yes, there are more homicides committed by other means. But it's not about the overall quantity of deaths that the ban concerns. It's about the number of deaths in a single incident. Most homicides involve people who know each other. But when a death is caused at random, no "personal cause" at hand, it angers people the most. These assault weapons make it very easy to just kill a bunch of people all at once. It empowers the killer to murder many at will. THIS is what the ban is all about. Because if we don't do anything to stop it, the fear (and right so), is that more people will seek to do the same thing. Troubled, desperate people who see this as an effective means to vent their anger.
They were second
graders. Give a man a hammer and he can kill them until he gets tired, and without raising the alarm that the sound of a gunshot would cause. The largest school massacre in US history didn't even involve a single shooting victim. It was all done with explosives planted by a school employee over months.
Banning the sale of assault rifles won't stop such people, because they plan, and they improvise. Europe has school massacres too, as does Russia where civilian rifles are hardly even allowed (my town has more than all of Russia combined).
In response to the tragedy, Newtown voted down even the idea of providing an armed guard. If a schizophrenic nutcase wanders in and breaks the glass to grab an axe, they're still screwed.