Five boys aged 12 to 14 who pelted a father with sticks and stones as he played cricket with his son have been found guilty of his killing.

Ernest Norton, 67, died from a heart attack after at least two of the missiles struck his head. One stone, the size of half a brick, fractured his cheek bone.

Mr Norton and his son James, 17, had neared the end of their Sunday afternoon bowling practice outside a leisure centre in Erith, Kent, when up to 20 youths approached them.

Without any provocation, the boys started yelling insults, telling Mr Norton to "go back to the old people's home". When he confronted them, they launched a hail of missiles.

"It just seemed they wanted to pick on someone," James told the trial.

As he collapsed with a heart attack on the outdoor tennis court, his son James ran to fetch his mother, Linda, from the gym. She could only hold her husband's hand, calling his name, as he lay dying with his head in a pool of blood.

An off-duty policeman tried to save Mr Norton and two doctors arrived by air ambulance, but he died at the scene.

The five boys burst out in tears and clung to their mothers when the jury found them guilty of manslaughter and violent disorder yesterday.

But their reaction was in stark contrast to their behaviour throughout the month-long court case.

Judge Warwick McKinnon was forced to order the parents to keep the boys under control after complaints from court staff who saw two of them had been seen hanging out of windows.

"It has been brought to my attention that the defendants are wandering around unaccompanied and conducting themselves in such a way that staff members are worried that they may well get up to mischief," the judge said.

One of the 14-year-olds fell asleep during the trial.

The boys, one only 10 at the time of the attack, were the youngest ever defendants to appear at the Old Bailey.

They belonged to a gang called TNE and had met up with another group of youths for a fight earlier that day.

As the boys ran off after attacking Mr Norton, a nearby resident heard one saying: "I think I got him." Another neighbour saw a boy crying as he struggled to keep up with the rest, and calling out, "He's dead, he's dead."

Mr Norton, a former engineering draughtsman who looked after his two children full time, never saw the birth of his first grandchild days before the end of the trial.

"He would have been thrilled to have a grandchild, especially a granddaughter," his wife said.

David Fisher QC, prosecuting, told the jury: "This was a completely unnecessary, pointless and random attack."

Mr Norton, who had a triple heart bypass operation in 1977, had been in good health until "the stress and trauma of abuse and a physical attack" made him vulnerable to a heart attack, the court heard.

Of the boys, Mr Fisher said: "Their youth is no defence. They were quite old enough to know that to abuse Ernest Norton and his son was wrong and that to throw stones and pieces of wood at them was wrong."