When I went to my GI and asked about
diet she said it what I eat makes no difference,
I did not believe it and went and researched many "health" diets. There were many that looked good and I selected one called the Specific Carbohydrate Diet or SCD. I am not sure why I selected this one, but it works for me and is much more important to me than medication. The diet put me in remission.
Some of the diets I looked at are Paleo, Low Res, FodMap, Makers, All worth considering in my opinion.
A great book that fits will all of the above is Healing Traditions by Sally Fallon. Also Life Without Bread. This book details why low carb is good for folks with CD (although I am not sure if this applies to children).
You may also wish to go to pecanbread.com. It is a site for children and parents doing SCD. They have lots of great advice for parents.
There is no single answer as to the best diet for folks with CD, we are all so different. Some here even have experienced little or no gain with diet changes, but in my experience it is very worth looking into.
I know I am blessed that diet works so well for me and I hope it does for your child also
Take care
David