Once there was a squarish book, of simple color photographs of familiar nursery objects, that endured for decades because it was so unequivocally and unsurpassingly a first book. These two squarish, heavy cardboard volumes (with rounded corners, on the side of the opening) are in that line of descent--the more outstanding (and rudimentary) because Hoban plumps a single object in bright primary colors--sock, sneaker, bib--in the middle of each page of What Is It? and the simplest, most natural of multiples--five fingers, four quarters of an orange--on each page of 1, 2, 3. The latter, indeed, begins with a single candle on a birthday cake--this is a book for children at that age--and follows, in a cross-reference to What Is It?, with two sneakers. Many libraries of course steer clear of board books--and there'd be no place to put a pocket except on the back cover. But for display, or for the diversion of visiting tots, it's worth considering--while parents, caretakers, and kin will seize upon the books--especially 1, 2, 3: a looking-and-learning knockout with its red numerals, number-words, and dots-to-count.