ALTHOUGH THE NUMBER of children's cookbooks on the shelves these days is overwhelming, skimming through their pages with a critical eye and a few pointed questions in mind can quickly narrow the choice.

The same basic criteria apply to children's and adults' cookbooks: Are the instructions clearly worded? Are they specific (especially for children)? Are there informative illustrations, at least for complicated steps? Are cooking terms explained? With those requirements met, the differences among children's cookbooks, as in the new ones described here, lie primarily in style, theme and level of sophistication.

For very young cooks--those who can read, but require close adult supervision in the kitchen--the What to do with . . . series is a happy find. Each book of the series-- first published in the Netherlands--centers on one food: What to do with . . . Vegetables (Barron's/Woodbury, $3.95. Ages 6-10) is the most recent U.S. release, preceded by volumes on . . . Fruit, . . . an Egg, and . . . a Potato.

French-born author Francoise Blanchet's choice of recipes, as well as the color-splashed illustrations by Rinke Doornekamp, capitalize on a child's absence of inhibition and a professional's desire to bring imagination and a certain elegance to food, even on this elementary level. All the basics are there--eggs are scrambled, boiled, or poached, potatoes baked, mashed and fried--but each book also includes some dressed-up variations of the old standbys. Egg whites become the snow on a festive, if primitive, baked Alaska; potatoes turn into one-dish meals; a Waldorf salad's traditional mayonnaise dressing is lightened and sweetened with whipped cream; and cucumber halves are scooped out and stuffed with sardines mashed to a paste with butter.

Even when Blanchet cannot resist slipping in "toy food," she does it well, keeping it simple: pear mice with cherry noses and licorice tails; bread boats heaped with cottage cheese and radish slices.

None of the What to do with . . . books has more than 18 recipes, all of them brief but complete, and each accompanied by step-by- step, how-to illustrations.

Less thorough, but appealing to young cooks because of its theme, is The Wonderful Wizard of Oz Cookbook (Macmillan, $7.95. Ages 7-12) This one falls into a trap common to cookbooks based on a non-food theme: in an attempt to entertain, it sacrifices logical organization and careful recipe selection.

Certainly the book is clever in spots. Recipes bear names like "Cowardly Lion Quivering Gelatin," and "Haystack Sandwiches."

But author Monica Bayley has arranged her 90 recipes in an order that only the Wizard himself could fathom, and many of the recipes are not detailed enough for young cooks. A corn-sausage casserole calling for three cups of cooked noodles, for example, neither explains how or when to cook them, nor advises the cook to consult the package directions.

The appearance of the book, with its cartoon-like illustrations by W. W. Denslow, suggests that its recipes are "easy." However, a recipe for pork chops and cabbage wedges braised in bouillon calls for frying a large sliced onion in a pot already occupied by six pork chops, eliciting cries of "There's no room in the pot for the onions, Mommy." Still another recipe calls for two cups of raw wild rice, an extravagance that even the wise and loving Aunt Em would hesitate to hand over to the little ones.

Further up the age ladder come two superb international cookbooks: Many Friends Cooking: An International Cookbook for Boys and Girls, by Terry Touff Cooper and Marilyn Ratner (Philomel/Putnam; paperback, $6.95. Ages 10-up), published in cooperation with the U.S. Committee for UNICEF, and What's Cooking? Favorite Recipes From Around the World, by Ruth Ann Hayward and Margaret Brink Warner (Little, Brown, $10.95. Ages 10-up).

Anyone familiar with Many Hands Cooking, which preceded Many Friends, is acquainted with these authors' instructive and informative style. In Many Friends, there are sections such as how to use chopsticks, fancy napkin foldings, metric and U.S. measures, herb lore ("Pepper was first used some 4,000 years ago in India") and "Around the World Eating Customs" (it is bad luck to talk, hum or sing while dining in Ghana). Each recipe is preceded by a paragraph or two offering cultural and historical background on the food and eating habits of that nation, and the flavor of each country is captured magnificently in Tony Chen's full- color illustrations that have the familiar primitive quality of many UNICEF Christmas cards.

Many Friends is spiral bound, a surprisingly rare feature, and recipes are clearly written, thoroughly thought out and, of course, highly varied in character. There is everything from a simple yogurt from Kenya called a Banana Smoothie, to comparatively intricate Deram Fiti (wheat-sprout pancakes) from Pakistan, with all recipes coded with one to three spoons indicating the degree of difficulty.

Although the authors skimp on how-to illustrations, there are a few pertinent ones, such as how to fold a burrito and slice flank steak across the grain.

What's Cooking? takes an entirely different approach to the international theme. Geared to teen-agers, the book is a collection of recipes contributed by teen-agers, most of whom are immigrants to America or whose parents or grandparents immigrated. Recipes represent some 32 countries and four regions of the United States. The authors' intent, they say, is to "take the lid off" the melting pot that is the United States by asking the question: "What is American food?"

The book is sensibly arranged alphabetically by country. It is not illustrated, and it is not a "how-to-cook" book, but the directions are clear.

What's Cooking's special charm is in each contributor's brief anecdotal preface to his or her country's recipes. In the hands of Hayward, an editor by profession, and Warner, who writes for young readers and runs an inn in Newport, Rhode Island, the young cooks' words give an arresting reality to the "foreign" cultures from which the recipes come.

Silvia Lopez, whose empanadas tested out beautifully, explains that "We hardly ever ate breakfast in Argentina," and describes her "first encounter with Cheerios. . . . I ate it non- stop for days." Adolpho Obiang allows that in Equatorial Guinea, "city" food bears the influence of Spain, which ruled his nation until 1968, but that his pepper soup with fish reflects his personal preference for the African food of the countryside. Several of the contributors note with candor that they are "not great" cooks, or that "cooking may not be my first love," but "eating good food is."

Last, but not necessarily most "grown up," is Knead It, Punch It, Bake It (Crowell. $10.50. All ages), which, while written in simple language, is valuable for breadmakers of almost any age. As the title suggests, authors Judith and Evan Jones emphasize the fun of making bread, using words such as "alive and bouncy" to describe its elasticity.

Getting down to business, Jones and Jones are clear, straightforward and friendly. Instead of requiring readers to wade through a long scientific discourse--as adult bread books so often do--before starting to cook, they integrate the essential definitions and general instructions in the first recipe (Basic White Bread). Their advice is eminently practical for young cooks: "If you're shorter than about five feet two inches, you may find it easier to knead on a table or another surface that is an inch or more lower than the usual counter height."

The book continues with 33 more recipes for common and unusual breads such as pear bread flavored with ginger and honey, oatmeal bread in traditional double-decker English cottage loaves, a Scandinavian rye made with fennel, caraway and orange. Each is preceded by a brief, informative introduction on the history or lore of the bread.

There is a rich assortment of quick breads-- banana-carrot, blueberry-orange, gingerbread --along with bread-like goodies such as hush puppies, doughnuts and pancakes. There is an especially good section on shaping different kinds of rolls, accompanied--as are all recipes --by Lauren Jarrett's precise black and white line drawings.