The toddler is said to be in a stable condition in hospital following the incident. The pitbull, which did not belong to the boy’s family, has been put down with the owner’s consent, police said.
Police said the incident happened in Kilmarnock, East Ayrshire, at around 8pm yesterday.
The boy was taken to Crosshouse Hospital in the town for treatment, where he remains.
A 25-year-old man is to be reported to the procurator fiscal in connection with a contravention of the Dangerous Dogs Act 1991.
It is understood the dog was owned by the boyfriend of the 3-year-old’s mother and the attack happened in the dog owner’s mother’s home.
Neighbours today spoke of their shock following the attack in the garden of the home in the quiet street in the Bellfield area of the town.
One neighbour said: “There have never been any problems with the dog, it was always fine as far as I could tell.
“The family are devastated.
“Police were here last night all over the garden, and I think the dog has been put down now.
“It’s terrible what happened but it was just a horrible, horrible accident, that’s all.”
Another dog-owner walking two french bulldogs in the street said: “I didn’t even know anyone had pitbulls in this area, I thought they were banned.
“Any dog has the capacity to bite anyone but it’s absolutely terrible about the wee boy.”
A police spokeswoman said: “Police Scotland received a report of a three-year-old-boy having sustained a facial injury after being attacked by a pitbull dog in a garden in Kilmarnock.
“The child was taken to Crosshouse Hospital where he received surgery to a facial injury.
“He has been detained and staff described his condition as stable.”
A series of measures to improve safety around dangerous dogs are being considered by the Government after a spate of incidents in recent years.
Universal microchipping, licensing and the wearing of muzzles in public areas are suggestions up for discussion in a public consultation, which was launched after the First Minister met with a group of parents whose children have been attacked by dogs.