While Mother cautions eponymously from the next room, Marvin plays rambunctious imaginative games (cowboy, magician, pirate, etc.) around his sibling's crib, finally falling asleep in the crib. The illustrations for this commendable debut are unusual for their energy and subtle use of vivid color; the concluding twist—the baby wakes Marvin—provides a satisfying irony. Especially appropriate for a parent/preschool group. (Picture book. 3-7)