THIS CHILDREN'S ISSUE of Books World is full of adults - expert adults - telling other adults what children will like, what children should like and therefore what children will be encouraged to read. So here we turn to the children themselves, to children of elementary school age, and let them say what they think of three of this spring's new picture books.

The children who contributed to this article are all pupils of the Peabody/Edmunds Elementary School on capitol Hill, an inner-city public school with a varied and fully integrated student body, and I should like to thank those children, their principal Mrs. Veola Jackson and their language arts teacher Mrs. Roberta Conwell, who made this whole project possible.

The children were given three books and asked, simply, whether they liked them or not, and why. No one had any problem with the first question, but they "why" proved harder and relatively few children could articulate abstract reasons for their preferences. They liked the books or they didn't and that, as far as they were concerned, was an end to it. When they did have reasons, however, they were definite and straightforward. Many just enjoyed the books, copied out some of the words with infinite care, or just drew a happy picture. Few authors could ask for more.

The hit, the real star among the three, was unequivocally. How The Rooster Saved the Day, by Arnold Lobel, pictures by Anita Lobel (Greenwillow/Morrow, $6.95). A simple narrative of good guys versus bad guys pushed to hilarious extremes - the broader the humor the better as far as the kids were concerned. The rooster, whose job it is to crow up the sun each morning, escapes from the robber who wants to plunge the world in perpetual darkness, by pretending to be deaf and by acting like different farm animals. A moral tale where the robber gets his just deserts. All ages seemed to be pleased with that.

David, aged five, thought the story was fine the because the rooster was in the mud with the pigs. Brian, aged six, thought the story was nicest where the rooster crowed for the sun. Matthew, aged four, liked it when the rooster pushed the sun up, and when the robber said he was going to eat the rooster up. Tracy, aged five, thought the story was funny and liked it when the rooster made the robber run away. Tasha was the single dissenting voice among the five-year-olds. She thought the story was silly. When asked why, she was succinct, "Because the rooster did so may silly things."

The older children took a more sophisticated view of the story as a whole, although interestingly neither age group made any comment on the very striking illustrations in the book. They seemed to treat the story as a whole without separating words and pictures. Felitia, aged nine, wrote "I like the book very much. It shows that a robber cannot get away with everything." Rachel, aged eight, was another fan: "I think the story was very nice. Why? Because I like the idea of the rooster waking up the sun." Desiree: "Yes, I liked the book because the rooster kept on saying that he were other animals that he wasn't." Maureen, aged eight, concluded with a sentence that should encourage wouldbe writers everywhere: "It was nice because somebody made up the story."

Least popular of the three books - or hardest for the children to comment on - was The Dog Who Wrote on the Window with his Nose and Other Poems, collected by David Kherdian, pictures by Nonny Hogrogrian (Four Winds, $5.95), an appealing collection of short poems with beautiful colored illustrations calculated to charm a child's heart. But the kids just couldn't get excited about it. Most expressed their dissatisfaction as young children often do, by saying nothing. Some were quite impressed, but all the same voice objections. Aaron, aged eight, wrote "I like some the poems and some were boring. I like the book."

"Once Upon a Tree," a two-verse poem by Theodore Roethke seemed to touch a common chord. Adriano, also aged eight, wrote "I liked this story because some of it was funny like when it said once upon a tree at the bottom of the page and the man standing on his head on the next page."

Kievette liked the book but accused it of false pretenses, "I really did like this book, because I like the poems in it," she wrote. "And in another way I don't like it because it has to many poems and it really doesn't have any thing about a dog writing on a window." So much for cute book titles.

Seven Little Monsters, by Maurice Sendak (Harper & Row, $3.95; paperback, $1.95), is a slim quasi-counting book by the creator of the immortal Where the Wild Things Are. One adult critic has described it as "an indifferent effort" and reproached Sendak for having "his attention elsewhere." The children found its slightness manageable and approachable, especially the younger ones. Small children don't ask for sophisticated story lines - Seven Little Monsters has almost none - but Christoper "liked the story because it seems like fun." He added a small piece of advice for the author: "If I wrote the story, I would have gave them a name." Six-year-olds were pleased with the simple little book "I loved this book" wrote Nicole. "I liked it," seconded Leah. Ten-year-old William was typically cryptic: "The Seven Little Monsters was good too, and the one I like best is the one that fly and the one that creeps in the night. The end."