When you have a child with autism or ADHD and you choose to implement dietary changes, the question becomes - do we all do it or just the one child? I'll discuss this in reference to GFCF (gluten free, dairy - casein free), but it could also be broadened to any dietary changes you wish to make.
Depending on your personal situation, you may or may not choose to have a strict GFCF household when you initially convert your special needs child onto this diet. Having personally experienced both sides of this topic, I'd love to share with you some of the pros and cons of each.
Strict GFCF for Everyone
Pro - When the entire family "goes GFCF" (or whatever dietary changes you choose), it shows complete support for the one who needs it.
Pro - Eliminates the risk of cross-contamination when you are preparing, cooking and serving foods that contain these ingredients.
Pro - There are additional health benefits (other than reducing or eliminating ADHD and autism behaviors and symptoms) that can be experienced while on this diet. There are over 300 symptoms of gluten intolerance alone! If the whole family goes GFCF in support of the one who needs it, they will likely be surprised at how they benefit as well.
Pro - Simplifies life. One meal plan, one shopping list, one set of cookware and utensils, etc...
Con - If you are restricting everyone's diet due to food sensitivities of one person, it could be that others are unnecessarily eliminating these foods. (Of course, see point 3 above - these changes will most likely benefit them as well!)
Con - It is more expensive to purchase specialty food items and if everyone eats them, you will need more of these items. (Sticking to whole foods, not based on breads and dairy, instead of using GFCF alternates eliminates this con!)
Con - If your children are aware of the fact that they must follow the special diet because someone else needs it, there could be resentment. (Inform the family you are making general healthy changes and don't pin it on the one child.)
Mixed Diet Household
Pro - This is more flexible. When having other people in your home who aren't familiar with GF alternates, you have "regular" food on hand for them. (Although it never hurts to serve your GFCF foods and show them how good they really are!)
Pro - For families with more than one child: If you only have to be strict with one child's food, it's not as complicated trying to organize food for every event, outing and meal away from home. (Although, once you create a routine for one, it's easier to implement for everyone.)
Pro - Because you are more aware of cross-contamination issues, it's more likely to be easier on you when around foods not in your diet. You already have plans in place for keeping food pure.
Pro - Easier on the budget. (This can be outweighed by the cost to keep extra equipment... )
Con - The possibility for cross-contamination is high, especially with younger children who spill, make more mess while eating and don't yet clean up after themselves. (The older your children are, the easier this gets, but the risk is always there, even with adults.)
Con - There is opportunity for the GFCF child to sneak foods that shouldn't be eaten. (This is a possibility for any child who is away from constant supervision, of course, and the older the child is, the more freedom they have over their food. Awareness of what the food is and how it affects them is key to avoiding this.)
Con - There is a greater need for organization to separate foods, have a place for acceptable foods, and know which food is for what diet type, label it all, etc...
Con - Must have extra sets of cookware, utensils and be super diligent to not use the wrong item for the wrong food.
Con - Must buy multiple versions of the same foods or cook more than one version of a meal, which can be time-consuming and complicated.
Con - The child following the special diet alone might feel left out. (While this is a fact of life one must accept on a restricted diet due to food sensitivities and allergies, it's nice to know one is supported in their own home.)
As you can see, there are many reasons one might choose to keep a strict GFCF household or allow mixed dietary plans. Some of the pro reasons for one choice are simply the con for the other choice, just presented in the opposite perspective.
You may see a general trend in the pros and cons and my comments on each and realize that I am generally pro- keeping it strict GFCF in the home. While each choice may have more pros or cons listed, it's not the amount that counts. What counts most is what matters most for you.
Your unique needs and family lifestyle are more important that someone else's opinion. Do what works for you now. You can always change it if it doesn't work best for your family.