Yes, have done that, but it has been done in a large family(as you can see in my signature). I have never done it with one adult and one child. But, we have ordered half the meals of our family and split them. I have felt a bit funny about it, but they do what you ask for. There was one restaurant in Italy(Epcot that isn't there now) that the waiter was very rude about it, but if that is your order, it is not against the rules.
We split outside of Disney more and more all the time. Some restaurants charge an extra plate fee for splitting. But we usually order an appetizer(because we love them) and an entree. When they kinda look at us questionally if that is all and if they understand us right. We say, yes could you please bring the appetizer out like usual and the entree out with no extra plates please. They are like, ok are you sure you don't want an extra plate? We have always managed to skirt around the extra plate fee, by ordering two items and no extra plates.
I don't think Disney does or lets say the majority of them I don't believe do. I am thinking, their might be one or two that might say that. Just have to see if anyone says they have had a problem or decide to be bold and see for yourself.
It seems hard at first because it is out of the norm, but once you get used to it, it makes sense to be:
1. Using your credits wisely for your purposes
2. Not wasting food
3. Not overeating, because you were taught to never waste food.
4. Just plainly getting more bang for your buck!
It is up to you, and how much you eat, or for that matter eat a bit and save room for the things that look awesome, but I am never hungry to eat!!!