Rumination to negative affect has been linked to the onset and maintenance of mood disorders in adults as well as children. Responses to positive affect have received far less attention thus far. A few recent studies in adults suggest that responses to positive affect are involved in the development of both depressive and hypomanic symptoms, but thus far no study has investigated their role in childhood mood problems. The purpose of the present study was to validate a child version of the Responses to Positive Affect questionnaire and examine the extent to which responses to positive affect prospectively predict mood symptoms over a 3-month interval. The Responses to Positive Affect questionnaire for Children was found to assess two types of responses to positive affect: Positive Rumination and Dampening. Both subscales showed sufficient internal consistency and moderate stability over a 3-month interval. Low levels of positive rumination and high levels of dampening were concurrently associated with depressive symptoms, over and above responses to negative affect. Importantly, low levels of positive rumination also predicted increases in depressive symptoms over a 3-month interval over and above baseline symptoms in children reporting high levels of stress. Both positive rumination and dampening were positively related to concurrent hypomanic symptoms and high levels of positive rumination predicted increases in hypomanic symptoms over a 3-month interval over and above baseline symptoms in children reporting high levels of stress. The results underscore the added value of assessing responses to positive affect in addition to responses to negative affect.