Writer Jenny Sullivan knows all about bullying. Her eldest daughter was horribly picked on in both her primary and secondary schools. But the most horrendous week of Mrs Sullivan’s life came later when she was asked to run a writing workshop in a school where bullying was endemic.

“In the event it was fairly horrendous. The entire school gave off an aura of unhappiness - bullying seemed evident from the tiniest children upward,”

recalls the mother-of-three and prolific children’s author,” she said.

“It was an awesome responsibility for the school to give me, and I was so conscious that I was walking on very thin ice.”

The children’s stories reduced her to tears on several occasions. And the Cardiff author made them a promise that she would write about their experiences in the hope of ending the misery for others like them.

The resulting book, A Guardian What? (Pont, pound;5.99), will be launched next week at Llandrindod high school, in Powys. Some years earlier, Mrs Sullivan’s eldest daughter, Kirsty, had become the victim of bullying.

“Three girls set up a campaign of harassment. They put used tampons in her locker, and plastered notices over it on her 18th birthday that said ‘Happy Birthday - hope you die’ and other such things.

“Initially I advised her to rise above it, but it got to such a pitch that I made her promise to talk to one of the staff.”

It was advice she had given Kirsty when she was in primary school and being picked on by two older boys who had stolen her breaktime snack and were smacking her.

“Nobody likes to tell tales, Mum,” Kirsty had protested.

“The snitch mentality is always the hardest thing to combat,” says Mrs Sullivan. “I made it perfectly clear to my girls that, in certain circumstances, telling tales is not only permissible, it’s advisable.”

In both cases it stopped the bullying, as it does in A Guardian What? when heroine Tali finds herself at the mercy of two older girls.

Physically small and without friends in a new school where few speak Welsh, her first language, she becomes a target. Tali appeals for a guardian angel only to get Atchy - a second-rate guardian demon. But when Atchy communicates Tali’s problem to her classmates, the youngsters join forces and end the torment.

A little girl in a Rhondda primary school Mrs Sullivan once visited confided a similar woeful tale of constant bullying but did not want to tell anyone.

“I knew she had read my Magic Apostrophe books so I asked if she believed in magic,” she said.

“She did, and a bargain was struck: if the child told her the bully’s name, she would put a spell on him to make him stop.

“I probably shouldn’t have done it, but it was all I could think of,” she admits. To this day the child does not know that all it took to end her bullying was a word with the headteacher.