The title conjures up a delightfully scary childhood game that must be universal. Here, ``It'' is a blue, furry, elephant- size creature that climbs in a window, tends to leave mayhem in its wake, does such imaginative things as ``organize your shadows'' or ``blossom in the winter,'' and is a source of glee to the children who romp with it through a cluttered basement, in the midst of their school play, or at the beach. Somehow, adults never seem to notice it, though they are often astonished by what occurs in its presence. Geringer's brief, nicely cadenced text is amusingly suggestive, if a bit enigmatic; the real fun here is in Truesdell's ebullient illustrations of irrepressible kids and their bumptious, endearing companion. (Picture book. 4-8)
