The family of Shawn Seesahai has said that “justice has been served” after the Court of Appeal increased the sentences of his two murderers, believed to be the UK’s youngest knife killers.

Three judges ruled on Thursday that the eight-and-a-half year minimum terms of the life sentences given to two boys, who are both now 13, were “unduly lenient” and increased them to 10 years.

The two boys, who cannot be identified, were both aged 12 when they fatally attacked Mr Seesahai, 19, in Wolverhampton on November 13 last year, and were sentenced in September.

We recognise that justice has been served today for the murder of our beloved son, Shawn, and we welcome the Court of Appeal’s decision

Lawyers for the Solicitor General told a hearing in London that the sentences of both boys were “unduly lenient” and should be increased, stating the killing was a “particularly serious type of case”.

Following the decision, Mr Seesahai’s family said: “We recognise that justice has been served today for the murder of our beloved son, Shawn, and we welcome the Court of Appeal’s decision to increase the sentences of those responsible from eight-and-a-half to ten years.

“Shawn’s life was taken in a brutal and senseless act of violence. He was attacked with a weapon carried with clear intent, leaving us devastated and haunted by the thought of what he endured.

“While no sentence can ever bring Shawn back, we feel that today’s decision better reflects the gravity of the actions that took him from us and acknowledges the immense loss we live with every day.

“We hope this outcome sends a strong and clear message that carrying and using knives will not be tolerated.

“We are grateful to everyone who supported the review of this case and to the Attorney General’s Office for ensuring that justice was pursued.

“As we continue to honour Shawn’s memory, we remain committed to raising awareness about the dangers of knife crime, in the hope that no other family has to endure the pain we carry.”

Anguilla-born Mr Seesahai, who was living in Birmingham, was stabbed through the heart and lungs with a machete and suffered a skull fracture during the attack on Stowlawn playing fields, with one of his wounds measuring 23cm deep and almost passing through his body.

Both boys blamed the other for inflicting four wounds with the blade, but were unanimously convicted of murder following their trial at Nottingham Crown Court in June, and were described during their sentencing as the country’s “youngest knife murderers”.

They are believed to be the youngest defendants convicted of murder in the UK since Robert Thompson and Jon Venables, both aged 11, were found guilty in 1993 of killing two-year-old James Bulger.

High Court judge Mrs Justice Tipples had previously ruled that the defendants – known only as BGI and CMB – should be protected by anonymity orders, saying their welfare outweighed the wider public interest in open justice and unrestricted reporting.

Sentencing the pair, she said Mr Seeshai had “everything to live for” and described his murder as “horrific and shocking”.

We have, with some reluctance and sadness, come to the conclusion that the minimum terms imposed by Mrs Justice Tipples were unduly lenient

In a victim impact statement read to the sentencing hearing, his family said they were haunted by thoughts of how scared he must have been when he was killed.

They also described his murder as tragic, unexpected and senseless, and having been committed “for no reason at all”.

In written submissions for Thursday’s hearing, the Solicitor General told the Court of Appeal that the sentences were “significantly too short”.

Paul Jarvis, representing the Solicitor General in court, continued that the judge “made significantly too much allowance” for mitigating features.

Both boys attended the hearing via videolink from separate facilities, with BGI wearing a grey tracksuit and supported by two adults, and CMB in a white shirt and black tie.

Their barristers each argued that the sentences imposed were sufficient.

But in their ruling, Lord Justice William Davis, sitting with Mr Justice Bennathan and Judge Nicholas Dean KC, said: “We have, with some reluctance and sadness, come to the conclusion that the minimum terms imposed by Mrs Justice Tipples were unduly lenient.”

The judge said full written reasons for their decision would follow later, with the youths now set to spend nine years and 60 days behind bars because of time already served.

Following the hearing, a spokesperson for the Attorney General’s Office said: “This was a deeply distressing case. Shawn Seesahai was only 19 years old and had his whole life ahead of him but was brutally murdered over a minor disagreement.

“Knife crime is a scourge, and we welcome the Court of Appeal’s decision to increase the sentences of Shawn’s murderers, following the referral by the Solicitor General.”