Animals - especially pets - belong to our environment. Whereas studies of human-pet relationships mainly focused on the beneficial or therapeutic value of the pet to humans (e.g. inscrease self-esteem;help the cognitive and emotional development, be a social substitute), ethological approaches remain rare. It is important to consider a relation in a developmental view in which the encounter between human and animal is the first step. To fill up this lack of study, we developped an innovative standardized observation of the spontaneous first encounter between unfamiliar pets and people at subject's home. We hypothesized that people behave differently - according both to their own characteristics and the pet’s behaviors - highlighting behavioral profiles. To illustrate the method, we focused here on the approach of an unfamiliar guinea pig (Cavia porcellus) by 59 children (6-to-12-years-old, 32 girls and 27 boys). As expected, different profiles were defined: confident, expressive, fearful and carfeul profiles and children's behaviours were modulated by their characteristics too (sex, age…). Our test gives valid, reliable and repeatable method for understanding the encounter between an unfamiliar pet and people, both at adults and children age with typical or pathologic development. In conclusion, it must be widely used to adapt the animal assisted therapies to the patient’s characteristics and to highlight unique social characteristics both in typical and pathologic people.