The teen, who cannot be named due to his age, appeared in Liverpool Magistrates Court on Thursday over Monday's incident at a "Taylor Swift yoga and dance workshop" summer holiday event for children in the seaside town of Southport.
His case is due to be heard at Liverpool Crown Court later on Thursday.
As well as killing three girls aged six to nine, Monday's attack in the quiet town left eight other children with stab wounds.
Five remained in critical condition in hospital, along with two adults who tried to protect them, police said.
The 17-year-old boy was taken to a Liverpool Magistrates Court charged with murder. (AP PHOTO)
Large disturbances broke out in the northwest English town on Tuesday after false information was spread on social media that the suspect in the stabbings was a radical Islamist migrant, with anti-immigrant protesters descending on Southport town from elsewhere.
In London on Wednesday, thousands gathered near the prime minister's Downing Street residence, shouting, "Save our kids", "We want our country back" and "Stop the boats", as well as English football chants.
More than 100 people were arrested.
Police have said the attack was not terrorism-related and that the suspect was born in Britain, quashing speculation on his origins.
"Whilst these charges are a significant milestone within this investigation, this remains very much a live investigation," Chief Constable Serena Kennedy told a press conference shortly after midnight.
The people of Southport are reeling after the horror inflicted on them yesterday. — Keir Starmer (@Keir_Starmer) They deserve our support and our respect.Those who have hijacked the vigil for the victims with violence and thuggery have insulted the community as it grieves. They will feel the full force…July 30, 2024
Prime Minister Keir Starmer denounced as "violent thugs" those who clashed with police over the knife attack, saying they would "feel the full force of the law".
More than 50 police officers were hurt in the protests in Southport on Tuesday, when demonstrators set police vans on fire and dismantled garden walls to hurl bricks at officers.
In London on Wednesday, protesters threw flares and smoke canisters towards Downing Street.
Local people in Southport have denounced the violence.
"What I saw last night was absolutely appalling ... It was devastating and it's kind of taken away from actually what's gone on, which is the tragedy of those deaths," resident David Burgess told Sky News.
People in the Southport community have laid toys and floral tributes at the site of the incident. (AP PHOTO)
Hundreds of people in the community have taken part in vigils to mourn the slain children, and laid bouquets of flowers at the site of the incident.
Starmer, Britain's former chief prosecutor who was elected on July 4, was due to meet police leaders on Thursday to offer them the government's full backing following the violence.
"While the right to peaceful protest must be protected at all costs, he will be clear that criminals who exploit that right in order to sow hatred and carry out violent acts will face the full force of the law," his office said.
Taylor Swift fans have so far raised more than Stg325,000 ($A635,000) to help families of the victims and for the hospital where some of the children were being treated.
The American singer has said she is in shock over the "loss of life and innocence" and at a "complete loss for how to ever convey my sympathies to these families".
