This initial entry in a new Growing Up Stories series, focused on a child's first five years, is the latest from the ace chroniclers of early child development (Happy Birth Day!; It's So Amazing!). Each spread of the large-format book does double-duty: the bigger illustrations and bulk of the text track the growth of and family interactions with baby Benny—from his debut "Wha-wha-wha-whaaaaaaaaaaah!" to his first birthday party. Set off from the main text in a box with blue type and cartoon-like spot art is a kind of developmental primer, which answers the "whys" of the behavior spotlighted in the narrative. For example, a spread showing Benny mouthing his foot ("Benny looked like a pretzel when he did that!") explains that putting things in their mouths "helps [babies] learn whether something feels rough or smooth, soft or hard, comfy or not." The spot illustration shows a baby nipping his sister's nose. "He gwabbed by dose!" says a cartoon bubble, and the grandfather holding the child tells readers, "That's how he learns about noses." Emberley infuses his artwork with a spontaneity and humor that's perfect for the mood of the text. He renders the rapture of new parenthood as confidently as he does the skepticism of new siblinghood, and does a terrific job of depicting Benny's evolving physiognomy from newborn to toddler. Harris's sprightly but detail-packed style is once again pegged at exactly the right level for her young audience. Any growing family should find this volume a welcome addition. Ages 3-7. (Sept.)