Animal-assisted intervention (AAI) is an approach recently introduced into the hospital environment to improve the quality of hospitalization and provide important benefits for patients with chronic diseases and long-term hospitalizations. This work aims to verify the effects of animal-assisted activity (AAA) on the expression and quality of self-reported pain in hospitalized children and adolescents, while considering the subjects’ subjectivity. The participants were 17 hospitalized children/adolescents of both genders, aged 7 years and older, who complained of pain. Two therapy dogs were selected for the intervention according to the criteria of international protocols. The participants were asked an open question (“How would you describe your pain?”). After the question, an AAA session, which lasted between 5 and 10 min, was held with random activities spontaneously chosen by the subject. The open question was asked again at the end of the session, without the presence of the dog. Positive effects were observed in this population with regard to a decrease in self-reported pain. These results suggest that there is a possible symbolic elaboration of pain by the subject, in which the dog might represent acceptance and affection at a moment of great emotional suffering.