MORE THAN adult literature, children's literature is cumulative. Sure, grown-ups still read books from the past. But more children know Aesop than adults know Aeschylus. Ten know the verses in Mother Goose for every adult who knows the poetry of Father Hopkins. A hundred, maybe a thousand, devour Little Women for each older person who reads one of Lousia May Alcott's works of adult fiction -- say, her 1864 novel Moods.

The reason for this discrepancy is simple. The world of children changes less. Our grown world has been in flux for a couple of centuries. New ideas and new morals come almost as fast as new machines. Babies, quite unaffected by that, are busy counting their fingers and toes in the old way. Small children play with cats identical to Dick Whittington's. Adolescence brings the same body and mood changes it always has.

Because of this cumulative quality, children's literature is especially in need of anthologizing. And parts of it have long been anthologized. Fairy tales have done best.

But anthologies that cover the full range of children's literature have been few and, on the whole, poorly edited. They have been particularly weak in the matter of illustration, even though for young children the pictures are usually the most important part of a book. Some have even practiced the same kind of deception that fruit-sellers occasionally do. You know -- you buy a box of strawberries, and under the luscious top layer, the berries are small and green. So with some anthologies. Take the current edition of Margaret Martignoni's Illustrated Treasury of Children's Literature. Between pages 1 and 50, there are 35 full-color illustrations. Between pages 301 and 350, there are none at all.

Clifton Fadiman's World Treasury of Children's Literature is therefore particularly welcome. It is head and shoulders above any other children's anthology I have seen. It is superior in contents, in format, even in quality of printing.

But its greatest asset is probably Mr. Fadiman himself. Many children -- I was such a one -- vow to themselves that when they grow up they will never, never forget what it was like to be 7 -- or 9, or 12. They promise themselves that when they are parents they will not be insensitive the way they feel their own (otherwise quite nice) parents to be. Most forget all the same.

Mr. Fadiman hasn't. He may be 80 years old, but he understands 7, also 9. I can't say about 12 yet, because these first two books of the anthology are for younger children. Two more for older children will be published in 1985. The preface, notes, and comments are pitched just right. The directness and honesty are such as any child will approve. The contents are not arranged in the tiresome categories adults so love, but in an order of delight. There's no whiff of "It's good for you, dear."

What are the contents? Well, of course there are nursery rhymes and myths and fairy tales. There's poetry at random intervals. There are many whole books. Familiar ones such as Munro Leaf's Ferdinand and Ruth Krauss' A Hole Is To Dig. Unfamiliar ones like Gunter Spang's The House in Sunflower Street and Momoko Ishii's Issun Boshi: The Inchling. Parts of longer books such as Winnie-the-Pooh. Well-selected parts.

All this is not to say the book is flawless. It has several flaws. For one, Mr. Fadiman did quite badly with Greek mythology. The version of King Midas he chose, for example, is brief, flat, and boring. This is the more mystifying when you consider that Nathaniel Hawthorne's special for-children version is one of the early classics of our literature -- and being long out of copyright, wouldn't even have cost anything.

Another flaw is perhaps inevitable in the anthology form. Many books for young children depend heavily on timing, and timing in turn depends partly in pagination. That by necessity gets compressed in an anthology. Johnny Crow's Garden, for example, is here complete -- as to words, anyway -- but the whole thing gets jammed onto two pages. The sense of motion you get in the original is nearly lost.

The Little House fares better. The 40 pages of the original are here only shrunk to 11. The text is complete, and more than half of the original color illustrations survive. Even so, the book's impact is considerably diminished. There is no longer one event per page.

Worst of all, either Mr. Fadiman or his publisher commissioned an artist named Leslie Morrill to do a great many illustrations, especially for this anthology. That, as Benjamin Franklin once said, was an Erratum. Morrill had a few good ideas and many bad ones. Drawing Little Boy Blue and Little Miss Muffet as a pair of singularly unattractive monkeys I count as among the very worst. Morrill has ability, all right, and some of her Celtic-style marginalia are charming. But the cumulative effect of several hundred of her drawings is tiresome.

Fortunately, there are even more hundreds of the original illustrations -- by Wanda Ga'g and Munro Leaf and Jean de Brunhoff and Maurice Sendak and many another. There are enough so that the cumulative effect of these two volumes is indeed that of a treasury, of words and pictures both.