Appetizers are consistently included only on the deluxe dining plan.
On the regular dining plan, you can only get appetizers at:
Family style all you can eat restaurants
Fixed price restaurants like CRT or Akershus
Dinner shows
Restaurants that have separate three-course fixed price menus, with no substitutions allowed:
Le Cellier (lunch only)
Captain's Grill
Nine Dragons
Kona Cafe
Chefs de France
San Angel Inn (only one selection per course)
Fantasmic dining package or Candlelight Processional package
Marrakesh restaurant (Epcot) offers multi-course "feast meals that regular
DDP users can get with a surcharge, which is $5-$7 per person ordering depending on which "feast" you order.
On the deluxe plan, appetizers are not included with counter service meals or with breakfast.
Children age 3-9 get appetizers on either plan, but it must be an appetizer from the children's menu.
T-Rex does not include appetizers for adults on the regular dining plan. I don't have any idea what they offer for children.