Additional Study Information: To learn more, click the blue box "Do you qualify" and our study team will contact you. This research study will examine how an iPad-based cognitive training game combined with cognitive behavioral therapy (CBT) helps children with excessive worries and related repetitive behaviors (obsessive compulsive disorder). After completing the training, all children will be offered CBT, delivered by experts at no cost. This study will take place at Columbia University in Manhattan. Participation includes a clinical evaluation and questionnaires, 2 MRI scans, and cognitive training games on an iPad loaned to you, and compensation up to $400.