Detectives were today hunting for a sick letter writer who has threatened to abduct and abuse teenage boys.

The letter, which has sinister sexual overtones, was sent to a family in Holme Wood, Bradford, and contained an accurate description of one of the boys.

The writer claims he has been "contracted" to "keep watch" over them and warned the 13-year-old boy and his friends would be taken away to be "birched" and "taught a lesson" if he continued to "misbehave".

Police were called in by the terrified family and have now sent the anonymous letter to be examined by handwriting experts.

They have also given the family a 24-hour helpline number so they can immediately contact them.

Today the boy's mum Dawn McNulty (pictured), who has three other sons at home aged 15, eight and six, said she was afraid to let them out of her sight.

"It seems that someone has got a grudge against my children and that this is what they are going to do," she said.

"It is disgusting that you bring your kids up and then someone can threaten to take them away from you.

"One of my lads won't even go to the shops and another won't go outside unless he takes the dog with him.

"It is clear from the language and the way it is written that this is not just a note from a child. I won't even let my children play in a field over the road because I am so petrified.

"I am just trying to drum the message into their heads. I show them the news to make them aware of what is going on because I worry that they don't understand the dangers. All I can do is keep a close eye on them."

The anonymous letter, which had a Leeds postmark, was written on two sides of A4 in black ink. The writer claimed he had a three-year contract to keep watch over the youngsters, running until August 13, 2005. He warned the children would be "taken away at an unexpected time" and subject to punishment for their actions.

Mrs MacNulty, 33, said she believed the letter had been sent by a "sick person" living nearby. "I dare not let my children out of my sight," she said.

"It is just disgusting that you bring your children up and then someone can threaten to take them away from you like this. It is really heartbreaking to receive a threat like that."

Today a West Yorkshire police spokesman said: "An officer has visited the family to take details and a full investigation is now underway into this matter."

Ward Councillor Michael Johnson (Lab, Tong) said he was concerned to hear about the threats against the family.

"Mrs MacNulty has done the right thing to pass this on to the police and I will be contacting them to find out how their investigation is going," he said.

"This is the first incident like this that I have come across. Where there are incidents of anti social behaviour, my experience is that most people on Holme Wood do the right thing by reporting it to the police or the housing office."