THE POET Randall Jarrell only began to write books for children in the last few years of his life. But scenes of children, images drawn from fairy tales and fantasies, had always been present in his work. He wrote of war and deaths and aging, but he often wrote about them in terms of a child's failed expectations, as if amazed that life could grow so complex and so vicious. His poems are poems of disillusionment; "heartbreaking," Robert Lowell called them.

His children's books are possessed of this quality in a way that the children themselves rarely notice. And I suspect this is especially truly of Fly By Night , which has only just been published more than a decade after Jarrell's death. It evokes feelings in an adult that do not - I think could not - touch my six-year-old.

Fly By Night is about a boy named David. Each evening he floats out of his bed, drifting through his house, seeing the dreams of his father and mother and dog poised above their heads. He floats over the countryside and sees the mice dancing, and the sheep, who are also dreaming. ("All of them except one are dreaming that they are eating; that one is dreaming that he is asleep.")

David ecounters a mother owl who takes him to her nest and tells him an owl bedtime story. Then she takes him back to his own home and as she flies away he thinks: "The owl looks at me like . . ." But he can't recall. The next morning as his mother fixes him breakfast he thinks she "looks at him like . . ." But again he can't remember.

It's a frustrating tale with the same fascination but also the same horrible impotence that dreams often convey. David tells himself time and again as he drifts through the night that he ought to remember flying, because if he could he could fly in the day. But of course he can't. And the things he sees as he drifts through the night - the mice, the sheep - he longs to pet, but he is powerless to move his arms, incapable of touching them.

Jarrell once wrote that children ask of a story "what they ask of a dream: that it satisfy their wishes." But David's wishes are beyond his grasp, finally lost even to his memory.

"Do you like the story?" I asked my little boy while reading him Fly By Night . "Oh . . . sure."

When I had read him other books by Jarrell they set him laughing and giggling and begging me to go on. The Bat Poet , which I thought a mildly witty allegory of the literary world, was for him a simple, delightful bedtime story. The Animal Family , a more ambitious tale on every level, struck me as a gentle masterpiece, unforgettable, delicate and full of surprises. My son was also enthralled by the lonely hunter and his mermaid consort who assemble a family bit by bit, as chance gives it to them: first a bear, then a lynx, and at last a boy.

Maurice Sendak illustrated all three of these books. He drew delightfully animated inhabitants of a Southern back yard for The Bat Poet in 1964. In 1965 he decorated The Animal Family with haunting landscapes that never showed any of the characters.Fly By Night was one of the last things Jarrell wrote, just months before the evening in 1965 when he stepped out onto a highway to die. Sendak held the manuscript from publication for more than a decade, hesitating, it seems, to add his own vision to Jarrell's. In the end, as he said in a recent interview, "I drew myself as a baby in it - you can see me in my mother's arms in the book's only double-spread picture. And I may have taken a very lopsided and fanciful view of the story, but what I read into it was a great hunger pain - that longing I once felt in Jarrells The Animal Family - and I interpreted it as a looking for mama pain . . . Maybe it's my pain."

In his poem "Children Selecting Books in a Library" Jarrell wrote that "childrens' cries/Are to men the cries of crickets, dense with warmth/ - But dip a finger into Fafnir, taste it/And all their words are plain as chance and pain," and he went on to argue that the experience of escape, of change which children seek from their literature is little different from what the adult seeks from his.

But there is a difference, and it becomes clear in some of the last pieces Jarrell wrote: in his poem "The Lost World," in The Animal Family, and in Fly By Night .

In them we meet a child worried by the stories he's been told. In Fly By Night David is disturbed by his helplessness to remember or act; in the poem the little boy has read about and a mad scientist bent on destroying the universe; in The Animal Family , the hunter and the mermaid have told the boy that once he had another mother, before they found him in a boat washed up onto shore. But when the children seem disturbed, the adults reassure them. David's mother "looks at him like his mother." There is someone to say, "No, that's just play, just make believe." "Oh we just told you that . . . We've had you always."

This is the voice we want to hear, no matter how old we are - even more, if fact, as we grow older: the voice spoken by someone who knows all about us, saying that everything will be all right, this life, these worries, his helplessness is all a dream from which we will wake. It is the voice adults lie awake all night waiting to hear, but it onlycomes to chilren.