Footage released by the Metropolitan police shows three members of a south London gang carrying out an attack that nearly killed five-year-old Thusha Kamaleswaran Metropolitan police

Members of a street gang responsible for killing three teenagers in 20 months have been convicted of shooting a five-year-old girl and leaving her paralysed for life. Three of the group were convicted on Monday of wounding Thushara Kamaleswaran, who was caught up in a tit-for-tat shooting as she played in her uncle's shop in Stockwell, south London, in March last year.

Notorious in the area, the Gas gang is on a Scotland Yard list of 60 "high harm" gangs in the capital.

The chaotic grouping of young men, noted for their violence and a lack of remorse shown by those brought to justice, is also heavily involved in drug dealing, street crime, muggings and bike robberies in its heartland around Myatt's Fields in Brixton, south London.

Thusha, as she was better known, was shot during a spate of violence the pace and intensity of which heaped pressure on the police for many months and prompted fears that the gang is out of control.

At the Old Bailey, Nathaniel Grant, 21, Kazeem Kolawole, 19, and Anthony McCalla, 20, were convicted unanimously of wounding Thusha and another innocent victim in the shop at the time. Roshan Selvakumar, 35, who had been buying groceries, was shot in the face and has been left with bullet fragments permanently lodged in his head.

Paramedics fought to save Thusha's life, operating on her in the street after the bullet passed through her chest. Surgeons saved her again when she suffered a second heart attack in hospital.

She remains paralysed from the waist down and spends much of her life at Stoke Mandeville hospital, Buckinghamshire.

Now six, she will have to wear a brace and leg splints permanently, and may have to undergo repeated operations to prevent her spine curving. All her life she will be reliant on a wheelchair and will require round-the-clock assistance.

Three weeks ago extra officers were drafted into Lambeth as police imposed a random stop and search power – known as a section 60 order – across the borough after seven stabbings in five days culminated in the killing of 17-year-old Kwame Ofosu-Asare.

He was the third teenager in 20 months to die at the hands of the Gas gang, some of whom are aged as young as 12 or 13, whose members arm themselves with household knives or guns, riding around streets between Coldharbour Lane and Brixton Road on bikes.

In court on Monday, Thusha's mother said she still cries when she thinks about her daughter's fate and future.

"It's hard for all at home to see an innocent child hopping around like a rabbit, now paralysed," said prosecutor Michelle Nelson, reading Sharmila Kamaleswaran's statement on behalf of the family. "She was a playful child, always happy and smiling and was a good student at school."

Nelson added: "What she says is that the impact of this incident remains unbearable to the family.

"She cannot begin to explain the shock felt at the time of the shooting, that her children all were there in the shop, playing and dancing and within seconds of that Thusha was lying on the floor crying and saying she couldn't feel her legs."

As the statement was read out Grant hung his head in the dock, while his co-defendants displayed no emotion.

They were also found guilty of the attempted murder of one of two men who ran into the shop, Roshaun Bryan, who denies any involvement with gangs, and of having a firearm with intent to endanger life.

Judge Martin Stephens QC said he would sentence Grant, Kolawole and McCalla on 19 April. He told the jury he was considering whether to give them a life sentence or an indeterminate sentence.

Thusha's shooting came during a spasm of violence as the tit-for-tat war between the Gas gang and their rivals spilled over on the evening of 29 March last year on to Stockwell Road.

The perpetrators were pursuing what they thought was a member of a rival gang who took cover in Stockwell Food and Wine shop. Seconds later Thusha had been wounded by a bullet from a semi-automatic firearm.

In CCTV footage shown to the jury at the Old Bailey she is seen skipping happily in the aisle of the shop in a pink dress and red cardigan.

Outside, on separate CCTV footage, Grant is seen standing astride his bike, with his arm held out straight as he fires first one shot, and a few seconds later another shot. One bullet hit Thusha in the chest and exited through her back, passing through the seventh vertebra of her spine.

Thusha lives with her parents and siblings, a 12-year-old brother and three-year-old sister in Hainault, east London.

Her father, Jeyakumar Ghanasekaram, worked on the till at Stockwell Food and Wine, and Thusha's mother had brought the children to the shop to collect her husband when the shooting took place.

Scotland Yard officially refuses to talk about individual gangs by name for fear of "glamorising" their activities, and will not give details of the crimes committed by the Gas gang.

But there is known to be growing concern about the gang's activities, and the number of murders, stabbings and near-fatal attacks that members have carried out.

The spate of murders began in July 2010 when five boys knifed 15-year-old Zac Olumegbon to death outside his school. Five teenagers from the Gas gang have been convicted of his killing.

In May last year, 15-year-old Temidayo Ogunneye was stabbed to death as he tried to recover his mobile phone from members of the gang who had mugged him earlier in the day.

His killer, 16-year-old Nathan McLeod, from the gang, had been in court a few hours earlier, when he was given a noncustodial sentence for attacking another man with a breadknife.

On 2 March this year, following a spate of seven stabbings in five days, Kwame Ofosu-Asare, an A-level student from east London, was stabbed and killed in Brixton.

The convictions of the three gang members come a month after the launch of the Metropolitan police gang taskforce. Faced with rising levels of serious youth violence, and evidence that the capital's gang problem could worsen as the economic downturn bites, Scotland Yard has committed 1,000 dedicated officers to tackling the issue.

Speaking outside court, Detective Superintendent Gordon Allison, from the anti-gang taskforce, said: "This was a difficult and distressing case to investigate bearing in mind Thusha was just five years old – a baby – when she was shot and paralysed by Grant, McCalla and Kolawole."