At the table service restaurants, the childrens' menu has the selections for the 3-9 age group. Every menu has probably 2 appetizers, which are usually a salad, a soup or maybe fruit. Your child can select one and then order from the individual entrees offered. Or, there were (and probably still are) the "pre-selected" meals, which are an entree with side and appie. Often what we think is the side in this case is actually the dessert to check with the server.
When the dining plan first came out, restaurants that didn't have appetizers for kids let you select one for them from the adult menu. When Disney realized that it was giving away food far in excess of the plan value, they stopped that and revamped the menus so that all kids meals came with their own appetizer.
We don't care for most, the only one we like being the cheddar cheese soup at Le Cellier and the lobster bisque at Coral Reef.