THAT DID IT, now I'm angry. A friend left a mystery book called Skeletons on my desk with a note: "Did you write this? Do you know the writer well? Should you sue for agrandizement of character?" B. James Butters, the protagonist of this minor mystery, is a famous writer of children's books who calls his profession "kiddy lit," drives a classic Rolls Royce (and talks to it), dresses like Tom Wolfe, and is as coy as a juiced garden elf. He speaks in italics, thinks in CAPS, and dreads "growing up." B. James Butters is only fiction and, beyond a disparaging look at my own VW and wardrobe, I was merely piqued, but then I read three new books for young people and, damn it, I'm mad.

Kiddy lit may be easy to write, children's literature is not. The best can take its place with any writing, but it is a separate discipline, differing from adult literature to the extend that "illustration" differs from "fine art." (Illustrators always bring up this distinction when they're angry.) A writer for children is constrained to a simplicity and a sleekness of plot. A writer must have confidence to write simply, assurance gained from experience and reams of mistakes. The hardest and perhaps the best writing, for adults or children, has a Quaker plainness of thought and expression than in no way lessens its ability to carry ideas, moods, subtleties. Simplicity is a goal rather than a beginning, not a gift but a skill won with much effort.

All right, B. James Butters, you asked for it. Kiddie lit is not a bargain basement or a training field, and people who are still under four-feet tall have the same desires and rights to suspense, surprise, plot, finesse, imagination, and skills that taller citizens have. Further, Mr. Butters, they demand respect, and "that of the commonest goddamned kind."

The Cricket in Times Square began a series that might have been spared this sequel, Chester Cricket's Pigeon Ride. There is less than half a story here. Even readers of earlier installments will not feel keyed in to the cricket's unlikely world and curious friends. Little care is spent on supporting the motives or feelings of the cricket, his old friends in the subway, or his new friends, a coy, liberated hen-pigeon named Lulu whooo speaks in a pecuoooliar pigeon patois. The rationale for the story seems to be the aerial ride, a pleasant idea unfulfilled by George Selden's words or by Garth Williams' illustrations, both presentable but unimaginative, like efforts pushed for a short, mercantile deadline. These words and pictures do not carry the interesting matchbox world of a cricket-person or the vertigo of a pigeon ride among skyscrapers. It will take brighter tools to coax forth more sympathy for a Times Square cricket than for a New York cockroach.

Inspector Mouse is not a good children's book. It might be best to leave this brief declarative sentence stand but a skulk of other books written with a few "witty" adult references and a patronizing lack of content stands with it. The story itself (Mouse loses cheese, mouse finds cheese) is a weak half-hour's effort, totaling less than three double-spaced pages of inexpert prose that should put some editor at Holt, Rinehart and Winston in jeopardy. pAll the characters have mouse-names: Inspector Mouse, Pinstripe Mouse, Informer Mouse . . . over a dozen mouse names in three pages should have any reader standing on a kitchen chair shrieking. There is a lame running joke about cheese names that children won't get, but no other binding factor. It has no plot, no suspense, no surprise. Many of Ralph Steadman's drawings are superb, bold and colorful and, beyond that fact that he can't draw mice particularly well, successful. We can expect him to illustrate a better piece of writing.

The Lost String Quartet, written and illustrated by N. M. Bodecker, is a good children's book. Its sketchy, dim drawings are effective and fun. The story is a well-developed scenario for a Marx Brothers movie that relies on things children may understand better than adults: madness, inconsistency, and progressive mayhem. It is the story of the incomparable but improbable Daffodil String Quartet set loose in the wilds on a snowy night, of their numerous travails, and of their inevitable triumph as they perform an impromptu but admirably controlled Spring Quartet in E minor for String Beans, Alpen Horn, Tirelin, and Viola Constrictor.

There are genuinely funny lines here: When the lost quartet emerges from a manhole in the middle of a prison yard and is shuffled into an exercise line, cellist Sidney Periwinkle is worried. "Now the people who bought tickets for the concert will want their money back," Sidney mumbled. "They are not going to wait patiently in their seats for ten to twenty years." There is much intelligent lunacy and a quiet display of skill B. James Butters couldn't cough up on the best day of his well-heeled life. It points out that kiddy lit is written by adolescents for adults, and that children's literature is written by skilled writers for the children within all of us.