Instead, six-year-old John sat down to write a heartbreaking farewell letter to his small friend, one of 20 primary school students killed in the Newtown massacre last week.

In his child's scrawl, the first grader wrote that he would talk to Jack "in my prayers" in the letter, which was displayed at Jack's funeral in Newtown on Monday.

Photographs accompanying the letter showed the small boys, one with Jack draping his arm around his blond friend's shoulder.

"Jack, you are my best friend," John wrote.

"We had fun together. I will miss you. I will talk to you in my prayers. I love you Jack. Love, John."

USA Today reporter Yamiche Alcindor tweeted a photo of the letter, which has been shared more than 1000 times on the social networking site.

Children as young as five attended the funeral for Jack, a huge fan of American football team the New York Giants and, in particular, wide receiver Victor Cruz.

Jack was such a fan of Cruz that he was buried in a white jersey emblazoned with the number 80, Cruz's number.

Cruz, who has an 11-month-old daughter, learned in the aftermath of the shooting that Jack had idolised him and in the Giants' game that weekend, Cruz inscribed Jack's name on his football boots and gloves. "Jack Pinto 'My Hero,'” one read. “R.I.P. Jack Pinto,” said the other.

Meanwhile, a sixth-grade student in Utah took a gun to school on Monday, saying he wanted to protect himself against a possible school shooting.

The 11-year-old was being held in police custody on suspicion of possessing a dangerous weapon and aggravated assault, after other students at the Salt Lake City elementary school told police he threatened them with the gun.

The boy reportedly had an unloaded .22-calibre handgun and ammunition in his backpack, and waved the weapon at others during the morning recess.

The boy claimed his parents sent him to school with the gun for protection, which his parents denied, according to a spokesman for the school district.

Sales of bullet-proof backpacks also have reportedly tripled in the US in the wake of the Newtown shooting.

Amendment II, a Salt Lake City-based company that manufactures lightweight bullet-proof backpacks for children, including Disney-themed bags, said sales had gone through the roof since the Sandy Hook massacre.

"I can't go into exact sales numbers, but basically we tripled our sales volume of backpacks that we typically do in a month - in one week," Amendment II president Derek Williams told US magazine Mother Jones.

Meantime, the National Rifle Association, the biggest pro-gun lobbying group in the US, has broken its silence on the Newtown shooting, saying it was "prepared to offer meaningful contributions" to prevent future massacres.

It marked a sharp change in tone for the group.

"The National Rifle Association of America is made up of four million moms and dads, sons and daughters - and we were shocked, saddened and heartbroken by the news of the horrific and senseless murders in Newtown," the organisation said in a statement.

The NRA plans a news conference on Friday after staying silent out of respect for families in Newtown and as a matter of common decency, the statement said.

US President Barack Obama indicated he would support legislation restoring a ban on assault weapons and requiring background checks of buyers at gun shows as steps toward preventing more mass shootings.

Mr Obama would also consider backing restrictions on high-capacity ammunition magazines such as the one used by gunman Adam Lanza in the Newtown school massacre, the White House press secretary, Jay Carney, said.