Byron Edward Syvinski, 32,from Anchorage, Alaska, tried to steal the little girl's bicycle in broad daylight and then punched her so hard on the head she was knocked unconscious, according to police.
Witnesses then claim that he punched her several more times when she was lying on the ground and went through her pockets.
The girl, who was not named, was hospitalized in critical but stable condition at Providence Alaska Medical Center with head trauma, said Marlene Lammers, a police spokeswoman.
Syvinski was arrested at the scene on Sunday afternoon and, according to Ms Lammers, he was 'right there by the little girl'.
He was being evaluated on Monday at a local hospital and faces charges of assault and theft.
Before attacking the girl, Syvinski allegedly accosted a 17-year-old boy in the same neighbourhood. He is said to have grabbed a bag from the boy and started going through it before giving it back.

Syvinski lives in the neighbourhood where the assault occurred.
Up to now, he has apparently not clashed with neighbours, Ms Lammers said.
'He's lived there about ten years and has had no problems,' she said.
State court records show that Syvinski has a long history of criminal charges and convictions, including theft, firearms violations, assault, robbery and domestic violence.
but this sounds more like programming to me.