I thought I'd share some words of wisdom given to me by Anart on the subject of changing a child's diet.
Quote "I won't presume to tell you what you should do with your son - he's your son. I would like to point out, however, that since he is your son you ARE responsible for his body until he is an adult.
You are the parent - you are in control of his body/health until he can do it himself.
With all the troubles he's had at his young age, he absolutely needs to be off all gluten, sugar, dairy, processed foods and almost all carbs. If you can take this opportunity to completely change his diet - while he is still so young - you have a chance of improving the rest of his entire life. If he keeps eating the way he's eating, he'll be chronically ill for the rest of his life. Just my two cents."
Back in September, I changed the entire family's diet to low carb/paleo. In the beginning, it was hard. There were many bad habits that needed to be broken, but as time progressed and everyone started seeing the benefits with weight lose, more energy, less illness it became a way of life and not just a diet. I'd say the biggest obstacle for us was the social aspect of eating. Here in the US, fitting in and being accepted by peers is a major issue. My children want to be like the other children and with past experiences with my oldest being bullied and subsequentially ostracized from his main group of friends, I decided that there would have to be times where I would allow them to go off the diet, like a birthday party or a sleepover. So although I try my best for them, it's certainly not perfect.
I would say having a younger child would be an advantage. It will become all they know. There would be less social programming involved also. I would also say, the best thing you could do is stay current with your knowledge. New information keeps coming up. Read, research, try new approaches to old recipes and find staples you know your child likes that are healthy. That's just my 2 cents and I hope it has helped you in some way.