THE lad accused of hurling a six-year-old boy 100ft from an art gallery balcony is a mental patient who had slipped away from his minders.

The 17-year-old — who cannot be named for legal reasons — is said to have suffered from schizophrenia and is usually only allowed out of a secure home with two carers, sources claimed.

Horrified witnesses told how the child was snatched from his mother and thrown over a chest-high barrier at London’s Tate Modern.

The boy — who is French and was on a family holiday — plummeted from a tenth-floor viewing deck to a fifth-floor roof on Sunday.

Last night he was “critical but stable” in a hospital intensive care unit following life-saving treatment.

A youth — said by witnesses to have remained chillingly calm as the victim’s mother screamed hysterically — was arrested at the scene.

Early today Scotland Yard said a 17-year-old had been charged with attempted murder. He will appear in court this morning.

‘ODD BEHAVIOUR’

His odd behaviour was said to have distressed several trippers at the tourist attraction before the incident.

A former carer who worked with the alleged attacker last year told The Sun: “He’s one of the most difficult and challenging mental patients I’ve ever encountered.

“He is stockily built — about 5ft 10in tall — and gets angry when he is denied something that he wants or is told what to do.

“He’s not allowed out unless accompanied by at least two support staff.

“He’s also intelligent. I watched an edition of the TV quiz show The Chase with him once and he answered every single question correctly.

“Something must have gone seriously wrong at the Tate because he’s not allowed out unless accompanied by at least two support staff.

“There will have to be a serious inquiry into what he was doing there.”

Police were investigating whether the teenager absconded from his unit or bolted from staff escorting him on a day trip.

A Met spokesman confirmed: “Mental health is being explored as a line of inquiry.”

Det Chief Insp John Massey said: “We’re providing around the clock support to the little boy’s family as they wait for more news on his condition.

“At the moment, this is being treated as an isolated event with no distinct or apparent motive.

“There is no link between the victim and the male arrested.”