. . . is small but it carries a load of meaning, largely in the interplay between nonchalant text and pregnant pictures. Cherished little girl acquires, to her increasing disgust, a baby sister -- ""The baby got patted./ The baby got fed./ The baby got kissed/ on her soft little head""; ""I want a bird instead,"" says little girl. While parents tend baby, little girl tends bird; otherwise responsive, bird refuses to be lured on her finger until one day she tries to amuse baby. Both grow, baby sister gradually displacing bird as playmate. When bird becomes old and dies, the two bury him reverently, then go inside ""to see if their father would take them for a ride in their pajamas after supper."" The linkage of events over a protracted period approximates life but also diffuses the focus; put differently; what is closer to reality is also farther from fiction. Children may respond less immediately than to such separate probes as Baby Sister for Frances and The Dead Bird but the latent absorption is incalculable. Certainly this tries to put childhood upheavals in long-term perspective, an uncommon undertaking in a brief, terse, tender picture book.