``Moompa'' is Toby's granddad; ``Bomp'' is the appealingly relaxed clown toy he pushes in his stroller when they go to the park. As Toby plays, Bomp is seen in every picture, at first in the center of the action, taking his turn on the swing and the slide, but later forgotten when Toby falls and then gets involved in the sandbox—though Bomp's always visible, on the ground or being played with by another child or a dog. When it's time to go home, Toby and Moompa remember Bomp and, after retracing their steps, find him. The very simple, yet carefully constructed, story is told in just a few words, plus Hines's bright but unassuming illustrations, where lapsitting toddlers can enjoy spotting familiar activities and following Bomp's independent adventures. (Picture book. 1-4)