Susanne Strub's My Dog, My Sister and I has a four year old speaker who remembers his own babyhood, the coinciding arrival of his baby sister and his dog. Comparisons are interesting and very much the kind of things a young boy would note. Ellen Senisi's Brothers and Sisters is a photojournalistic accounting of what many brother and sisters think of their relationships. The range covers kids of all different colors, age differences, and feeling states. There are twins and adopted children.
Siblings close together and far apart.
A spectrum of brightly illustrated relationships. What might be really fun is to record your children's own story. A First-Year Record Book for Big Brothers and Sisters by Dian G. Smith. This sibling baby journal is formatted with illustrations from the Metropolitan Museum of Art's 1914 Le Journal de Bebe . There is plenty of room for comparisons, drawing, photos and feelings.