In an inquiry with young children at a small river beside a school in Cuenca, Ecuador, romanticizations of harmonious childhoods and pristine, even magical, river natures are in abundance. Using common worlds framings, this article interrupts purity in child-nature pedagogies. We argue that encountering the river as a site of contradiction, and as an inherently pedagogical contact zone, requires disrupting discourses of "purity" that separate humans from their vulnerabilities with/in mutual, already contaminated worlds. To do so, we revisit pedagogical documentation from our walks at the river, and put them in conversation with persistent anthropocentric logics and the vibrant life of plastics at this river. We also gesture toward the pedagogical dispositions that might be required to cultivate educational experiences that are situated in the midst of the problems and impurities that the world proposes.