Teens are the most active age which has to be maintained by parents by allowing them to play more out door games like football, volley ball ,basket ball, etc which is itself a great activity.Let them do chin ups if they like it and climb up and down the hills. Let them make more active than being a home worm.Encourage them to participate in school sports without worrying of the results. Free themselves to jog, swim, run in front of you or even you can accompany them to make them enjoy more. After the age of 16 years he /she can start exercising but it should be a light one rather than heavy weights and so. Also, fix a day or two in a month to have junk food as junk food also leads to increase in weight These of ideas will help to loose weight for your teen.