Query performance prediction (QPP) methods have primarily been tailored to mainstream users, thus relying on the traditional concept of relevance. In the case of children, however, relevance goes beyond content-based resource-query matching, which is why we gauge the performance of existing QPP methods in estimating the fit of resources retrieved in response to child-formulated queries. Outcomes from our empirical exploration of various QPP methods using a traditional and a child-focused definition of relevance on 2 datasets reveal the limitations in the adaptability of existing methods to the context of child information retrieval.