Ernest Norton was hit on the head by stones

Ernest Norton, 67, suffered a heart attack in Erith, south-east London, when he was pelted with stones and sticks by the group.

An Old Bailey jury heard Mr Norton was hit on the head at least twice.

The boys, now aged between 12 and 14, were found guilty of manslaughter and violent disorder. They will be sentenced on 19 October.

Mr Norton had set up stumps with his 17-year-old son James in a tennis court outside Erith Leisure Centre in February 2006 to practise bowling.

But they were approached by up to 20 youths who began shouting abuse including, "rubbish bowler" and "go back to the old people's home".

We were just keeping ourselves to ourselves... it just seemed they wanted to pick on someone James Norton, son Wife and son watched him die Parents told to control boys

Mr Norton tried to scare them off but they threw stones, rocks and pieces of wood at him and he collapsed bleeding heavily.

"We were just keeping ourselves to ourselves," James Norton told the court.

"It just seemed they wanted to pick on someone."

James and his mother Linda watched as an off-duty police officer tried to resuscitate Mr Norton but without success.

The court heard Mr Norton underwent a triple heart bypass operation in 1977, but since then had enjoyed a "fit and active" lifestyle.

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

He said "the stress and trauma of abuse and a physical attack would make him vulnerable to a heart attack".

The father and son were playing cricket in the tennis court

"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."

He added: "I expect they deeply regret the death and no doubt did not intend that he should die.

"But it was their joint course of conduct, quite probably with others, that caused his death."

Earlier in the day the boys, armed with a baseball bat, had met another group of youths for a fight, the court heard.

Only one of the accused, now aged 14, gave evidence at the trial. He admitted spitting at Mr Norton and that it was "stupid", "revolting" and "appalling".

He said he was only throwing stones to try to knock over stumps and wreck the cricket game, for a "bit of fun".

Nobody likes to see children standing in the dock... crying having been convicted of manslaughter Det Ch Insp Phil Adams Police reaction

He added the boys had ended up at the leisure centre because there was "nothing else to do".

Crown Prosecution Service lawyer Damaris Lakin said: "This case highlights the need for young people in gangs who engage in anti-social behaviour to accept responsibility for the consequences of their criminal activities."

After the case, Mrs Norton left the court with her sister Margaret Barraclough, 70.

Mrs Barraclough said: "We now hope for closure and to get on with our lives."

Det Ch Insp Phil Adams said: "Nobody likes to see children standing in the dock at the Old Bailey, crying, having been convicted of manslaughter.