This commentary serves as a primer for trainees and experienced researchers who are new to neuroimaging of pediatric clinical populations. Non-invasive neuroimaging is now possible across the entire lifespan and encompasses a wide variety of tools and techniques. Developmental neuroimaging has been a fertile research ground for advancing new techniques and innovating approaches for group comparisons, including of those with psychopathology. However, developmental neuroimaging is hard to do well, and three reasons why are discussed: 1) Biology is on the move in development, and neuroimaging techniques are challenged by the high variability over age and across individuals; 2) Many cognitive constructs of interest in both behavior and psychopathology are interrelated and fuzzy, causing difficulty in interpretation of neuroimaging results; and 3) neuroimaging of pediatric populations, especially clinical samples, requires several special considerations in design and execution to be successful. Through discussion of these points, and note of some creative solutions in recent work, we hope to encourage more to research basic open questions in the field, and to inspire adherence towards rigorous and reproducible science.