Cortical electrical stimulation mapping is often required to accurately delineate eloquent function before resective surgery for tumors or epilepsy. Although the technique is well established in adults, mapping poses special challenges in children that are addressed in this article. The concept of what constitutes a critical cortex is more difficult to assess, given the implications of plasticity and impact of deficits. Developmental factors affect the underlying neurophysiologic bases of responses to electrical stimulation, and evolving maturation requires adaptation of methodology. Furthermore, malformative substrates are the commonest substrate and often lead to aberrant representations of eloquent function.