''Sometimes,'' says renowned New Yorker cartoonist and children's book author William Steig, ''I start drawing without knowing what I want to do interesting things can happen that way.'' Fittingly, it was more or less by chance that Steig, now 87, was first drawn to writing for kids: A friend casually suggested it over dinner almost 30 years ago. ''The idea was appealing and it enabled me to give up work in advertising, which I'd always felt unclean about.''
After 25 books of which Zeke Pippin is the latest countless numbers of children and parents have entered Steig's vibrantly imagined, comically serious world. The critics have come round for a visit, too: Steig's Sylvester and the Magic Pebble won the 1970 Caldecott Medal; Newbery honors followed for Abel's Island (1977) and Doctor De Soto (1983).
Although he didn't write his first children's book until he was 60, his next project, a collection of cartoons for kids, is rooted in part in his earliest childhood memory: ''sitting in an automobile the new miracle then before I was 2, and being taken for a short ride.'' The book's title? Grown-Ups Get to Do All the Driving.