IT DOESN'T take long to figure out that ''A Day with Wilbur Robinson,'' will be anything but dull. When Wilbur greets you at the door, Lefty the octopus takes your overnight bag.
Once inside the house, you find an aunt playing with her train set (with a life-sized locomotive), a cousin walking the cats (who happen to be grown tigers) and Uncle Gaston sitting comfortably in the family cannon.
As Wilbur and the narrator set off in search of Grandfather Robinson's false teeth, they encounter each of Wilbur's bizarre relatives. In a favorite scene, Grandfather Robinson is in his lab with his friends Mr. Ellington and Mr. Armstrong, rehearsing with a dancing frog band.
''A Day with Wilbur Robinson,'' by William Joyce (Harper & Row, $13.95, ages 4-8) is a delight. Joyce's illustrations -- instantly recognized by fans of ''Dinosaur Bob and His Adventures with the Family Lazardo'' -- are a cunning combination of surrealism ,, and art deco. Each page brings another round of surprises, some of which won't be discovered until the fourth or fifth time through.
This is a book to be savored again and again. At the end, when the family gathers to bid the narrator goodbye and Wilbur apologizes for ''such a dull day,'' readers can't wait to be invited back.
Several other new books also encourage flights of imagination, with maybe a little mischief thrown in.
* ''The Stupids Take Off,'' by Harry Allard, illustrated by James Marshall (Houghton Mifflin, $13.95, ages 4-9) is the latest in a super series about the Stupid family: Stanley Q. Stupid, Mrs. Stupid and the two Stupid kids.
While Mr. Stupid is brushing his teeth with anchovy paste, he gets a telegram that Uncle Carbuncle is coming to visit. Mrs. Stupid lets out a blood-curdling scream, and the family takes off in its plane to avoid the offending uncle. Along the way, they stop in to visit a host of other relatives, all as stupid as the Stupids. Marshall's absurd cartoons match the slapstick text. It's guaranteed to get 5-year-olds gigging.
* ''What if the Shark Wears Tennis Shoes?'' by Winifred Morris, illustrated by Betsy Lewis (Atheneum, $12.95, ages 4-8) shows that maybe mothers don't know everything. When Stephen's mother comes to tuck him into bed, he worries that a shark may come and eat him in the middle of the night. She says they live too far from the ocean for that to happen, but Stephen's not so sure.
The shark could hitchhike, or steal a Ferrari, and find his way to the house. What if he has spare keys that would unlock the door, and what if he wears tennis shoes so he wouldn't wake up Stephen's mom and dad? Maybe Stephen's endless questions aren't so ridiculous after all, the surprise ending suggests.
* "The Stories Julian Tells," by Ann Cameron, illustrated by Ann Strugnell (Knopf Bullseye paperback, $2.95, ages 5-9) is a delight. The writing rushes you along through six tall tales told by Julian, whose fibs are great fun. A perfect read-aloud book, it's also a good read-alone book for third- and fourth-graders.
Julian's imagination conjures up magical cats, a mysterious fig tree and plenty of other mischief. Julian, who is black, shares a warm, trusting relationship with his mom, dad and little brother.
* ''Moog-Moog, Space Barber,'' by Mark Teague (Scholastic Hardcover, $12.95, ages 6-9) is the story of Elmo Freem, who gets an absolutely horrible haircut the day before the first day of school. He stays up late that night, watching a science fiction movie on TV and worrying about how much he'll get teased the next day at school.
Then he discovers a couple of space monsters in his kitchen (drinking milk straight from the carton, no less), and they take him in their flying saucer to the planet Moogie. There, Moog-Moog, the greatest barber in the universe, works for hours to fix the haircut. Back at home the next morning, Elmo gets a fitting surprise as he leaves for school.
* ''Mrs. Minetta's Car Pool,'' by Elizabeth Spurr, illustrations by Blanche Sims (Aladdin paperback, $3.95, ages 5-8) transports readers on a weekly adventure with the kids who car pool with Mrs. Minetta in her bright red convertible. The car -- with Mrs. Minetta's faithful black Labrador, Rambles, in the passenger seat -- can fly.