The increasing sophistication of social robots has intensified calls for transparency about robots' machine nature. Initial research has suggested that providing children with information about robots' mechanical status does not alter children's humanlike perception of, and relationship formation with, social robots. Against this background, our study experimentally investigated the effects of transparency about a robot's lack of human psychological capacities (intelligence, self-consciousness, emotionality, identity construction, social cognition) on children's perceptions of a robot and their relationship to it. Our sample consisted of 144 children aged 8 to 9 years old who interacted with the Nao robot in either a transparent or a control condition. Transparency decreased children's humanlike perception of the robot in terms of animacy, anthropomorphism, social presence, and perceived similarity. Transparency reduced child-robot relationship formation in terms of decreased trust, while children's feelings of closeness toward the robot were not affected. CCS Concepts: • Human-centered computing → Empirical studies in HCI; Laboratory experiments;