A Wandsworth mother who stabbed a teenage boy, mistakenly believing he had attempted to rape her son, was warned she faces jail.

The 31-year-old knifed the 15-year-old three times in the leg after her son phoned her in tears claiming he had been assaulted.

She rushed to the scene in Wandsworth after being told her 13-year-old boy had also been beaten up.

After the attack she jumped back in to her car and drove off, leaving the injured boy to get help.

Her son was driven to St George's Hospital, Tooting, for surgery on two wounds to his thigh and one to the right calf.

On Thursday she was unanimously convicted of unlawful wounding by a jury at the Old Bailey. She was cleared of the more serious charge of wounding with intent.

Adjourning sentence, Judge Giles Forrester QC said: “I have to decide what the appropriate sentence is and you are looking at a custodial sentence certainly. All the options the court has remain open to it.

“Be under no illusion this is a serious matter.”

The woman told police and the jury she believed there had been an attempt to sexually assault her son in St John's Drive, Wandsworth, on the evening of April 18 this year.

She said she was at a children's party when her brother phoned and said her son had been "rushed".

“He said a group of boys tried to beat him up and he said they tried to bum him,” she said.

“I asked what he meant and he said they tried to rape him.”

She then rang her son using a friend's mobile.

“He was crying. He said ‘Mum, that (boy) tried to rape me’.”

Her son and the victim had been sitting with their friends on a wall in St John's Drive, Wandsworth, when the play fight got out of hand.

The 15-year-old described how he was kicked in the groin by the younger boy before he put him in a headlock.

Prosecutor Matthew Farmer said: “When she was arrested later said she was under the impression that (the boy) had attempted to sexually assault her son.

“Whatever the reasons in her mind for the attack, it's quite clear that attack she did.

“She turned up in a motor vehicle, got out of the car, went up to the victim, stabbed him three times in the leg, got back in the car and drove off.”

She had “revenge in mind”, the prosecutor added.

All three wounds healed and 15-year-old has not suffered any long-term injury.

The defendant admitted confronting the 15-year-old but denied the stabbing.

She was convicted of unlawful wounding.

She had earlier been cleared of making threats to kill against the boy's mother.

She was released on conditional bail to be sentenced on October 15.