On Monday, police detained the Cardiff-born adolescent from Banks, Lancashire, and seized a knife.
A 17-year-old Southport boy accused of murder and attempted murder after a mass stabbing appeared in court.
The Hart Space community centre attack killed six-year-old Bebe King, seven-year-old Elsie Dot Stancombe, and nine-year-old Alice Dasilva Aguiar.
A “Taylor Swift Yoga and Dance Workshop” for youngsters aged seven to 11 in the beach town north of Liverpool was underway at the time of the attack.
The suspect, from Banks, Lancashire, but born in Cardiff, Wales, was apprehended on Monday.
His age prevents him from being named.
He faces three murder, 10 attempted murder, and knife possession charges.
Remanded into adolescent custody after appearing before Liverpool Magistrates’ Court on Thursday morning.
Late Thursday, he’ll appear before Liverpool Crown Court.
Mersey-Cheshire chief crown prosecutor Sarah Hammond said: “We remind everyone that the defendant is facing criminal proceedings and has the right to a fair trial.
Avoiding online reporting, comments, or sharing that could bias these processes is crucial.
“Our thoughts remain with the families of all of those affected by these harrowing events.”
Five of the eight other youngsters stabbed in the attack are in critical condition.
Two individuals, including an event organizer, are in critical condition after being injured.
After the Southport incident, a violent protest in London on Wednesday night led to over 100 arrests.
Flares, cans and bottles were thrown toward Downing Street gates.
Later, riot police tried to kick down a gate while engaging protesters.
The Metropolitan Police said those arrested were charged with violent disorder, assault on emergency personnel, and protest violations.
Some officers were minorly injured, it said.
The crowd screamed “Rule Britannia”, “save our kids,” and “stop the boats,” while some called Tommy Robinson.
Officers trying to calm protesters surrounded the Cenotaph military memorial.
Police car burns in Hartlepool
Eight individuals were arrested amid Hartlepool protests on Wednesday night.
Police arrested protesters for throwing missiles, glass bottles, and eggs at cops. Several officers were slightly injured.
Aldershot MP Alex Baker said there was “no justification for disorderly behavior, and the scenes do not represent Aldershot and Farnborough” as she condemned community violence.
The unrest in the capital, Hartlepool, and Aldershot follows the injury of 53 police officers in a mosque attack in Southport, Merseyside.
False online reports that the perpetrator in Monday’s stabbing crime was an asylum seeker who arrived in the UK by boat led to fights.