The first thing you need to understand is that you cannot force your child to lose weight. This tactic will only backfire and is particularly dangerous with teenagers. Nor can you take on the responsibility for their weight problem. That said, what can you do? (Assuming, of course, a trip to the doctor for a checkup has ruled out any medical cause for your child's excess weight.) Following are some suggestions and tips for helping your child deal with his or her excess poundage.