While falling into the epistemological debate occurring in the systemic current between the functionalist school and the phenomenological supporters, this article does not intend to expand on the ideological biases of these two currents. This article presents the ecosystemic perspective as a magnifying glass to observe the relations between the actors involved in the field of a child’s mental health, beyond these contexts. In the first part, we present some general considerations regarding the ecosystemic perspective through its seizure as an in-between of an epistemology that evolved from constructivist relativism to a behavioural determinism. The second part of this article focuses on the relevance of the use of the ecosystemic perspective in the study of relationships between the actors involved, by providing support to the children’s mental health services. In the third part, we will attempt to define the notion of relationship from an ecosystemic perspective. The fourth part will be a review of the meeting places within the field of a child’s mental health, taking the ecosystemic as an institutional and non-institutional issue. Finally, the fifth and final part will afford us the opportunity to de-compartmentalize the field of child mental health by illustrating the rational process of the relational ecosystem.