Generally children will experience some discomfort a few hours after having braces fitted- we suggest that they take some analgesics prior to their appointment but very little spontaneous pain is experienced, rather discomfort when they apply pressure to the teeth during function and discomfort from the physical presence of the braces.
Most kids do go to school- and in fact interacting with their peers often is the best way of distracting them form the adjustment process that may take 3-5 days.