Equine-assisted activities (EAAs) are considered a suitable innovative rehabilitative practice for children with neurodevelopmental disorders, including autism spectrum disorder (ASD). While standardized scales have been previously used as a tool to evaluate the effects of EAAs on different domains of functioning in ASD children, few studies have considered an ethological approach as a means to describe human–horse interactions in the context of ASD. In this study, we aimed to evaluate the behavior of 19 children with ASD, in comparison with 19 typically developing children (TD), during EAA sessions. We developed an ethogram from the video recordings to assess spatial relationships, social interactions, and communicative behaviors displayed by the child toward the horse, as well as the occurrence of problem behaviors. Results indicate that children’s behaviors during EAA sessions are modulated by sex and age, while previous children’s experience with EAAs appeared to improve interpersonal distance and horse handling. Results from this study highlight the importance of exploring children’s behavioral responses during animal-assisted activities through direct measurements. This may allow linking the quality/strength of the child–horse relationship to the benefits obtained by the child, particularly in the social/communicative domain, a core symptom of ASD.