I'm not convinced skipping out on only banana and cheese will make a difference here though! Start serving prunes and items that will get things moving, increase his water and fibre intake. Beans, beans, beans!!

Will the child being restricted care/notice if you don't serve him cheese and banana? If he's happy enough with a substitute then just restrict him.

My daughter (19months) is dairy intolerant (severely so). She is a foody and eats like a champ and she would seriously notice if she wasn't getting something. I just have a non-dairy variant of what ever I serve so no one really notices. She always gets a yellow cup so I can keep track of the rice milk to ensure she didn't find the wrong cup with real milk. She has soy yogurt instead of regular yogurt.

While there is a notable difference in the taste, look and smell of her 'fake' foods she doesn't care as she is happily scarfing down her yogurt.

At some point she'll have to learn that sometimes you just don't get the same...and it'll take some getting used to but right now I can give a substitute that keeps her happy.

All my baking and meals are made dairy free and I just add dairy items to the other child's serving when dishing out food so they still meet that food groups needs.