A five-year-old girl suffered "life-changing" facial injuries when she was attacked by her family's pet American bulldog as she bent down to kiss it.
Tanisha Hall's stepfather also suffered injuries to his arm as he grappled with the dog.
Police had been called to Hanemill Court, Northampton, at 1915 BST on Sunday.
The breed is not banned under the Dangerous Dogs Act, police added.
A spokesman for Northamptonshire Police said the dog "was contained at the scene" and had been put down by a vet.
Tanisha's grandfather, John Hall, said she was having surgery on her face and was expected to be in hospital for several days.
He said Tanisha had bent down to kiss the dog when the attack happened.