I had a similar problem wth my daughter when she was younger - about 4/5. I had to get really strict with her. Basically she got given what was on the plate she either ate it or she went hungry. This went on for a good few months. She never starved but she did go to bed hungry sometimes....guess what, she survived the night!!!!
She now only has wholemeal bread (not a problem) in her packed lunch. She has anything from tuna, sweetcorn and ex light mayo, cheese and light salad cream, dairylea light or reduced sugar jam in her sandwiches. Sometimes she might have ham or chicken, but not often.
She has 2 pieces of fruit (normally banana, plum, grapes or strawberries), a dairylea dipper or french fries/square crisps or WW cheese puffs or cheese curls. She has a carton of fruit juice, either apple or pineapple which is classed as one of her 5 a day.
For dinner she now eats pasta (wholewheat) with chicken or Jckt with Tuna, syn free sausages with mash, gravy and veg etc. Spag bol, saus casserole, SW burgers with SW chips and many other SW friendly meals and desserts including soups.
She still has 'normal' food and is allowed treats at the weekend. Most of them are home baked cookies, flapjacks or muffins instead of shop bought stuff. This way I also know that she isn't getting too many additives/preservatives either.
We only have sugar free juice or fruit juice cartons, semi skimmed milk or highlights hot chocolate.
I also make sure she's kept active. She has ballet once a week and swimming for an hour a week, with the occasional trip to the local park, walk in the woods or bike ride.
My daughter isn't on a diet (she's only 7 and a half - don't forget the half
) but I am determined that she is going to grow up with a healthy outlook on food. That treats are fine but food is for fuel and not for comfort. I don't want her to have similar problems as me when she gets older, I want to break the cycle.
Sorry for the long post
but it is something that I'm passionate about.