Open iTunes on your computer, log in with your account and find your purchased apps list, in the details of the app you will find a pocedure to get refund. But with those arguments you gave at the top there, you are not going to get any refund since there are ways in the iOS to prevent kids to download apps by mistakes. Try and comment with other arguments like unsuable on your device or something really hard which is not your fault but the app's fault or some thing.