10 yr old son over weight by about 1/2 stone because of eating huge school dinners (packed lunch not an option at his school, and despite talking about healthy eating I think he lies to me about what he has had at school as he has still put weight on). Whats the advice to help him loose this over the summer holidays? Do I tell him he's on a diet? Do I set weight targets? Is this likely to cause him more damage and make him overly body concious?