Some of the low sugar foods I've seen children enjoy in their lunchbox are; dips with veggies, jam made with fruit juice instead of sugar,easy yo homemade yoghurt, smoothies with fruit, yoghurt and milk, mountain bread with stuff on it.
I'm also reading an article on sugar at the mo in a new magazine called Nurture. It mentions that maple syrup is treated differently than sugar by the body so it could be an option to consider on breakfast.
Would muesli be an option for breakfast?