"We simply cannot allow easy access to weapons that kill," the president said in a speech as Suzann Wilson, the mother of a recent schoolyard shooting victim, stood at his side.
Mr Clinton urged support for a bipartisan congressional proposal to hold adults criminally responsible for allowing children access to loaded firearms. "We can't shrug our shoulders and say accidents happen, or some kids are beyond hope," he said. "That is a cop-out. Every one of us must step up to our responsibility.''
Speaking later at the American Federation of Teachers conference, Mr Clinton also announced plans for a White House conference on school safety in response to the six incidents in which 14 pupils and two teachers were killed between December and the close of the school year in mid-June.
"My life was changed forever," said Ms Wilson, whose 11-year-old daughter was one of the four children and a teacher killed by two boys at a school shooting in Jonesboro, Arkansas, on March 24.
The boys had broken into the home of a relative and taken several rifles and more than 500 rounds of ammunition.
"To every gun owner in America, I want to say: 'Please, please, for the sake of the children, lock up your guns,'" Ms Wilson said emotionally. "Don't let your gun become an instrument of murder. Don't let what happened in Jonesboro happen in your town."
The White House has also announced new regulations requiring gun shops to post signs stating that the "misuse of handguns is a leading contributor to juvenile violence and fatalities."