The teenager, who is from a nearby village in Lancashire, but was born in Cardiff, was arrested on Monday.
A 17-year-old boy, charged with murder and attempted murder after a mass stabbing in Southport, has appeared in court and been named as Axel Rudakubana.
Three children, six-year-old Bebe King, seven-year-old Elsie Dot Stancombe and nine-year-old Alice Dasilva Aguiar, died as a result of the attack at The Hart Space community centre.
A “Taylor Swift Yoga and Dance Workshop” aimed at children aged between primary school years two and six was taking place at the time of the attack in the seaside town, which is north of Liverpool.
Rudakubana, who is from a nearby village in Lancashire, but was born in Cardiff, Wales, was arrested on Monday.
Usually, the defendant, because he is aged under 18, would be granted anonymity.
However, in an “exceptional” decision, Judge Andrew Menary KC did not conceal the identity of Rudakubana – who turns 18 in six days.
The Liverpool judge said that doing so would allow others to “spread misinformation”.
“Whilst I accept it is exceptional given his age, principally because he is 18 in six days time, I do not make an order under section 45,” he said.
He added: “Continuing to prevent the full reporting has the disadvantage of allowing others to spread misinformation, in a vacuum.”
Rudakubana has now been remanded in youth custody, after he was charged with three counts of murder, 10 counts of attempted murder and possession of a knife.
Rudakubana appeared at Liverpool Magistrates’ Court on Thursday morning.
During the 55-minute court hearing, the teenager put his head down inside his grey sweatshirt and at times was seen rocking back and forth and side to side.