Oliver Stephens, known as Olly, was killed at Bugs Bottom field in Emmer Green, in the Berkshire town, on January 3. Reading Crown Court previously heard that Olly was convinced to go to the park by a 14-year-old girl, where he was then “ambushed” by the two boys and stabbed to death.
The girl admitted manslaughter while the two boys were today found guilty of murder.
All three will be sentenced at a later date.
None can currently be named because of their age.
The trial heard how Olly’s killers had fallen out with him because they believed he “grassed” on them to the brother of a boy they had mocked in a social media group chat.
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Alison Morgan QC, prosecuting, told the court that Olly had no idea he was about to be attacked.
“This was an ambush on him. A planned attack that was designed to put him in a vulnerable position,” she said.
One blade penetrated nearly seven inches into Olly’s back, and another wound in his chest was more than three inches deep, the jury heard.
An off-duty nurse walking her dog found the fatally injured teenager and attempted resuscitation, but he was pronounced dead at the scene.
Following the crime the killers tried to dispose of evidence and exchanged messages on Snapchat about the attack.
One of the boys described it as “the biggest mistake of my life”.
In a statement issued after the verdicts, Olly’s family described the stabbing as a “callous and cold-hearted act”.
“He left our home on that fateful afternoon with love and laughter in his heart, with the hope of a bright fun filled future ahead of him,” they said.
“Within 13 minutes of leaving the safety of his loving home Olly had left us forever.
“Two minutes was all it took to end him and cause us and our family catastrophic heartbreak.”
They added that Olly was “warm, kind, soulful, a deep thinker and a great carer to those around him”.
Both boys were also convicted of perverting the course of justice.