Preschoolers: not just very young children

Pediatric neuropsychologists are keenly aware through their didactic education and experiential background that principles and procedures related to adult onset brain disease and disorder are often misapplied to children. The adage ‘children are not just small adults’ captures this sentiment succinctly. Also increasing is recognition that procedures, interpretive rules, and algorithms applied to the evaluation of brain function in school-aged children do not translate optimally to preschoolers who have an even more immature brain (Baron & Anderson, 2012). Thus, another tenet deserving of instantiation is ‘preschoolers are not just very young children.’ This special issue was conceived as a broad-based forum for the dissemination of current and original research and commentary to highlight the range of advances being made regarding brain development and preschooler neuropsychological functioning. The only thematic directive to authors was that there should be an emphasis on children aged between 2 and 6 years. This is a maturational period that encompasses dynamic gains in brain growth and connectivity, and when subtle to profoundly adverse medical and psychological outcomes result when circumstances alter the typical trajectory. Communication was encouraged through a review of the literature, case presentation, critique of theory or methods, novel experimental paradigms, or report of application of rehabilitative intervention. The preschool years are highly instructive about early brain development and the maturation of emergent intellectual, neuropsychological, and behavioral functions. Yet, the effects of adverse health circumstances were long understudied by pediatric neuropsychologists who mostly investigated and evaluated children of school age or older, rarely preschoolers (Baron & Leonberger, 2012). This omission was fostered by a limited exposure to preschoolers in training and practice settings, a tendency for referral sources to rely on non-neuropsychologists for neurodevelopmental evaluation, few neuropsychological publications that informed about brain-behavioral function in preschoolers, and scarce age-appropriate tests and normative data. Consequently, neuropsychological knowledge about these formative years and the early neuropsychological trajectory associated with either normal or atypical brain development lagged. Challenges that further contributed to the gap in understanding developmental course included that present and future biophysiological, medical, epigenetic, psychological, social-emotional, cultural, and socioenvironmental influences will