Police have determined that the dog that attacked a three-year-old girl was of a breed that is prohibited in the United Kingdom.
Merseyside Police said the boy was sent to hospital after the attack outside a pub in Kirkby town centre on Saturday.
Her injuries were classified as "significant" but not life-threatening, and she was later released.
The dog, a Pit Bull Terrier, was described as "humanely destroyed" by the police.
A 31-year-old man from Ormskirk has been released under investigation after being seized on suspicion of affray and having a dog dangerously out of control in a public place.
The scene outside the Market Tavern pub in Newtown Gardens was packed at the time of the incident at 15:15 BST, according to police, who called for information.
Certain dog breeds are forbidden to own in the United Kingdom,
including the Pit Bull Terrier, Japanese Tosa, Dogo Argentino, and Fila Brasileiro.