Have i done my children more harm than good by feeding them non organic fruit and veg?

Not that I can see: The crucial thing for your child's nutrition is to get healthy food in. Fruits and veggies are very healthy and it's great that you are feeding them to your kids. I would worry less about food being organic or not and more about ensuring they aren't overloading on processed foods, carbonated beverages, salt and sugar. They really need to learn what foods are good and eating in moderation.