It's not just the buffet meals that you can't share. It is anything that is served as an "all you can eat" like the family style dinners at LTT and the skillet at Wilderness Lodge restaurant.
Anything that you order off a menu can be shared, whether counter service or table service. You'll end up ordering a beverage for your "extras," and possibly an entree and sharing the appetizers and desserts. Just a hint--some of the restaurants seem to have decreased the serving sizes. At the steak places (that list the weight of the steak) you'll know exactly what you're getting. At other places, it really depends on how much your party likes to eat. You can probably feed 6 off 4 dinners, but you might end up ordering a little extra. 5 off 4 dinners will be NO problem at all.
Just re-read your post...sharing with one adult, one child should be FINE.
You will get 2 checks if you order anything extra. One will show the dining plan credits used and the number remaining. The other will show the cost of the additional items ordered. That can be paid for with cash, credit card, or room charge. Just remember to add the tip for the extra items. It will help your server if you tell him when you order what you are ordering off the plan.
They don't frown on sharing--they are actually very helpful with it, sometimes making suggestions on menu items that are a little larger, etc. Bringing the extra plates is no problem.