A commenter in the thread about Cho Seung-Hui's psychiatric evaluation points to this statement from the Brady Campaign to Prevent Gun Violence:

It shouldn't take a school shooting or an inner-city neighborhood shooting to make us realize that American children are more at risk from firearms than the children of any other industrialized nation. In one year, firearms killed no children in Japan, 19 in Great Britain, 57 in Germany, 109 in France, 153 in Canada, and 5,285 in the United States.

For the U.S. figure, the Brady Campaign cites "Centers for Disease Control and Prevention, National Center for Health Statistics, unpublished data from the Vital Statistics System, 1997." According to the CDC, however, the number of children and adolescents under age 20 killed by firearms in 1997 was 4,223, down from a high of 5,833 in 1994. The Brady Center figure presumably is for one of those years in between, so I'm not sure what the "1997" signifies, unless it's the date when the data were unpublished.

In any case, note that the "children" killed by firearms include older teenagers, among them 18-year-olds and 19-year-olds, a.k.a. "adults." Judging from the breakdown in 1998 (I can't find comparable data for 1997), more than 80 percent of gun deaths for the under-20 group involve teenagers 15 or older. About 58 percent of the gun deaths that year were homicides, and these included drug dealers shot by other drug dealers, violent criminals shot by police, and other noninnocent nonchildren. About 33 percent of the gun deaths were suicides; 7 percent were accidents.

For the international comparison, the data should be expressed as rates (i.e., taking population into account) rather than absolute numbers. And they should cover all suicides and homicides, rather than just those committed with guns. If it turns out that people in Japan kill themselves just as often as people in the U.S. but use different methods, the availabilty of guns seems less significant. Likewise if the murder rate in the U.K. is just as high as the murder rate in the U.S. In fact, the Japanese suicide rate is twice the U.S. rate, while the U.S. homicide rate is several times  the U.K. rate. Deadly violence is more common in the U.S. than in the U.K. across the board, with and without guns. The extent to which gun control laws, as opposed to other differences between countries, can account for such differences in rates of deadly violence remains a matter of controversy, to put it mildly. 

Dave Kopel analyzed gun controllers' "do it for the kids" strategy in a 1993 Reason article that, with a few details updated, could easily be published today.