Former Army Corporal Barney Alcock, 81, who suffers from dementia, was left drenched in blood and his face covered in bruises after telling them to stop throwing berries against his window.
His wife of 57 years, Thelma, was on the phone with the police when she looked outside to see her husband on the ground, his glasses shattered.
She said: “There is no such thing as respect for elders nowadays from youngsters, and I was horrified to find what they had done to Barney.
“He’s not eating and he cannot remember what happened to him. It’s just awful to think that a gang of kids would do something like this.”
Mrs Alcock went to tell the youths off around 9.30pm when she heard banging on the windows of their home on Redbourne Road and saw berries splattered across them. However the youths swore at her and said: “Call the police, see if we care.”
Barney went outside, spoke to them and they left. But a few minutes later they returned. As he crossed the road to talk to them, his wife was on the phone to the police.
She said: “I turned around to see him lying on the ground covered in blood and the boys running away.”
Yesterday Mr Alcock made light of his injuries, saying he had suffered more in the Korean War.
He said: “I have had a lot of people ringing me up to see how I am. I made a lot of good pals in the war.”
Mrs Alcock, 76, said: “We can’t thank enough the people who have come around to help us and offer us support.”
Ted McGuinness, from the charity Dementia UK, said people with dementia could be particularly vulnerable, adding: “This story is a sad reflection of certain sections of society these days.”
Police said a 14-year-old boy had been arrested and released on bail.