The purpose of this study is to learn if measures of brain activity are different in children and adolescents with depression who are in different stages of treatment. This is important because it may identify a biological marker for depression that could one day be used to identify depressed children who would benefit from certain treatments (medications for example), or to monitor how well treatments are working. Brain activity measures(known as cortical excitability and inhibition) will be collected by Transcranial Magnetic Stimulation (TMS). TMS is a noninvasive (no surgery or implants) brain stimulation technology which can make parts of the brain work without putting any wires or chemicals into the body. Measurements will take place over one 3-hour visit. This study does not provide any form of treatment.