If you don't have a felony conviction, or various other disqualifying issues, it takes anywhere from ten minutes to ten days, depending on the locality, to purchase a rifle or handgun.
I'll ask another question - how easy/difficult is it for an adult in your country to buy a knife/car/whatever that can be used to kill people?
These are horrific events, whether they happen in Connecticut or Scotland (http://news.yahoo.com/scottish-town-shares-agony-u-school-tragedy-182038462.html) with guns, or China (http://en.wikipedia.org/wiki/School_attacks_in_China_(2010%E2%80%932011)) with knives and hammers. But they pale in comparison with the number and tragedy of single deaths that occur daily. Children are killed in car accidents, playground accidents, by parents, caregivers, and other children, in horrific and tragic ways. But, because they happen one or two at a time, they're a footnote in a local newscast and quickly forgotten. Nothing is done about them.
Heck, even the events of Sept 11, 2001 here in the US were a statistical blip - the 3000 people killed in the attacks are roughly the number of people who die every month in car accidents in the US. And yet we treat it as a national day of mourning, and disassemble our freedoms, to prevent it from happening again.
We as Humans grossly overreact to the extraordinary, and become accustomed to the ordinary. 20 Children killed with a Gun? Time to ban all guns. 40000 infants born in the US every year with Fetal Alcohol Syndrome (http://fasdcenter.samhsa.gov/documents/WYNK_Numbers.pdf), and we show a few public service announcements on the TV. Which is the greater tragedy?