Sing, Little Mouse is in the same key as Listen, Rabbit, and youngsters who hearken to the one will likely respond to the other. A towhead who's heard of a mouse that can sing importunes his family until father brings home a big book about mice and the two discover that the ""white-footed, light-footed"" Deer Mouse is a sometime singer. Following the clue of a Deer Mouse's tracks in the snow, the boy finds its hole, then, when spring comes, camps overnight with his brother nearby. A rainstorm sends them scurrying home but (""Can you guess what I saw/ in my very own house?"") the mouse has come too, in a sleeping bag, and favors the boy with trills and twitters before he's returned to his home. The most tangible, most forceful illustration shows the Deer Mouse magnified up front; most of the others, in color and black-and-white, are in a vein of misty lyricism that's Symeon Shimin's signature. Aileen Fisher's long narrative poem is similarly vaporous, even vapid. But the pair have their staunch adherents.