We investigated children’s understanding of mental life by analyzing attributions of perceptual, cognitive, affective, and other capacities. 200 children (7-9y) and 200 adults evaluated the mental capacities of beetles or robots. By assessing which capacities traveled together when participants disagreed about these controversial “edge cases,” we reconstructed the latent structure underlying mental capacity judgments from the bottom up—a novel approach to elucidating conceptual structure among children. For both children and adults, factor analyses revealed a distinction between social-emotional, physiological, and perceptual-cognitive capacities, hinting at three fundamental ways of explaining and predicting others’ actions: as social partners, biological creatures, and goal-directed agents (each involving related forms of both “experience” and “agency”; Gray et al., 2007). Relative to adults, children attributed greater social-emotional capacities to beetles and robots, suggesting that intuitive ontologies of mental life could be critical for making sense of children’s developing understanding of the social world.