Parents have called the stabbing of a 13-year-old boy in Reading “utterly senseless” as they laid floral tributes to a boy called Olly outside a school.

A group of mothers said their children were “devastated” at news of the boy’s death, saying they attended Highdown School together.

Four boys and a girl aged between 13 and 14 and are being held on suspicion of conspiracy to commit murder, Thames Valley Police said.

Officers were called just before 4pm on Sunday following reports of a stabbing in Bugs Bottom fields, Emmer Green.

The boy died at the scene.

One man, who declined to give his name, said his wife was walking their dog through the park on Sunday afternoon and saw a boy on the ground with several people gathered around, trying to give him first aid.

The boy’s face was “very white”, his wife told him.

Several mothers and their children laid flowers at Highdown School on Monday afternoon with cards.

They said their children were “devastated” and called the killing “senseless, utterly senseless”.

One card read: “Fly high Olly, love you loads, night night. We’re all gonna miss you. Our angel Olly, gone way too soon, you didn’t deserve this, in my heart forever.”

Another read: “Dearest Olly, Taken way too soon, you were such a lovely lad. Loved by many. Thinking and sending love to your family at this sad time.”

Police stood guard at a large cordon surrounding Bugs Bottom fields, with forensics officers seen around a small blue tent erected in the middle of an open field.

The scene is less than a mile from the school.

Another dog walker told the PA news agency she went through the park at around 3.30pm on Sunday and saw a group of youths standing around near woods, describing the scene as “slightly unusual”.

She said the park area has been “heaving” with joggers, walkers, metal detectorists and families in recent weeks.

Senior investigating officer Detective Superintendent Kevin Brown, head of Thames Valley Police’s Major Crime Unit, said: “This remains a very active investigation and a large scene-watch remains in place.

“We have arrested five young people in connection with this tragic incident, but I would urge anybody who has any information surrounding what happened yesterday to please make contact with Thames Valley Police.”

Police Federation chairman John Apter said of the incident on Twitter: “Horrific, so many lives will be shattered by this. Society does indeed need to take a look at itself.”