I am a long-time type 1 diabetic (36 years on insulin) without complications. I don't think that it makes any difference whether your child eats regular meals or variable meals with snacks as long as you know how to count the carbohydrates and adjust insulin accordingly. Obviously, those who eat according to a set meal plan have their lives simplified by not having to do the math for every single meal, but some folks prefer to have the flexibility of being able to eat what they want to and adjust the insulin.
As for foods with high glycemic index, common sense and good eating habits mean that you don't make up your daily diet with these foods, but if a child's glucose levels are low, then this is a better kind of carb to eat than one with complex carbs because they may digest too slowly to bring his glucose levels up quickly. So I find it best to stock both kinds of carbs in my pantry and eat the ones that are appropriate according to what my glucose levels are doing at that time.
I maintain tight control, and I know that this is hard (and sometimes even unsafe) to do with a child whose activity levels may vary greatly from day to day. But the key to keeping your child healthy is to try to keep those glucose levels as normal as possible without risking severe hypoglycemia.
My eight year old son, who was diagnosed more than two years ago, does follow a set meal and snack routine. He has breakfast, lunch and dinner, plus snacks at 10 a.m., 2 p.m. and before bedtime. He's to have 50-60 grams of carbs at meal time, and 20-30 at snack time. The only restriction he is under is that he must drink diet soda or Crystal Light (no regular drinks with sugar -- except juice when he is low), and must use sugar-free pancake syrup. I don't particularly pay attention to high glycemic foods. I just try to make sure each meal is generally healthy, with a balance of carbs, proteins and veggies or fruit. Obviously, he's not a long-time diabetic, but his A1C numbers have been good and he is otherwise in excellent health.
I am a volunteer and a mom of a type 1 diabetic. When it comes to my daughters diet, she eats normal food, the only things that we keep in our house that is sugar free is sodas and crystal light. Our doctor believes we should treat her as a child first and a diabetic second. With her being on the pump it has made this easier as we count her carbohydrates and give her insulin accordingly,
When she was on shots we did the same it just meant that she would occasionally decide between two things because if she really wanted something special it might have meant an extra shot of insulin, but we always from day 1 let her decide as it is her body.