A two-year-old girl needed hospital treatment after a dog bit her on the face in Howden, East Yorkshire.
Three girls aged 15 to 16 were walking a white West Highland Terrier in Howden Park, where dogs are prohibited, when the attack happened.
Humberside Police said the toddler was playing with the animal when it became aggressive and bit her.
She was left with scratches and a puncture wound to her cheek and was taken to Goole Hospital for treatment.
The child's mother spoke to the teenagers but no details were exchanged.
Police would like to speak to the three girls, the dog owner and anyone who may have witnessed the incident.