Boise Police say the attack happened March 27 at a parking lot on the 1300 block of South Broadway Avenue.
Officers say the boy was inside a van with the dog and two other children when the dog attacked.
The six-year-old was taken to the hospital with what officers called severe facial injuries. The other children weren't hurt.
Police say the dog's owner, Christopher Anderson, 24, was inside the nearby business and had left the children alone with the dog.
Officers say the children were in Anderson's care and that he is an acquaintance of a parent of the children.
Police say that immediately after the attack they were told the dog was running loose in the neighborhood so they set up a perimeter and started searching.
Officers say they found the dog in the backyard of an acquaintance of Anderson's, where he took it after the attack.
Police say the dog, a pit bull, was taken into custody at the Idaho Humane Society.
During their investigation, police say they found evidence that the dog had been aggressive in the past and that Anderson knew about it.
BPD also says that there is also a prior history of injury to a child involving Anderson and the children in the van.
Because of this, police say the children have been placed in the custody of Idaho Health and Welfare.
After Boise Police turned their investigation over to the Ada County Prosecutor's Office a warrant was issued for Anderson's arrest.
Police say they located him at a motel near the Boise Airport on July 5 and took him into custody.
Anderson has been charged with five counts of felony injury to a child and one count of resisting or obstructing officers.
He is being held in the Ada County on a $500,000 bond.
He is scheduled for a preliminary hearing July 18.