Inevitably perhaps, the co-authors of The First Twelve Months of Life (1973) and The Second Twelve Months of Life (1977), who together direct the Princeton Center for Infancy and Early Childhood, have moved on to the next stages of development; but the stage-by-stage format appropriate to the first two years (if disturbing, even then, to parents whose children don't ""keep up"") is a faulty vehicle for dealing with the great variations in growth and acquisition of skills between ages two and six. The book is at its best, indeed, in the two opening, all-embracing chapters. ""A Minicourse in Child Development"" knowingly introduces key concepts, major theorists (Erikson, Mahler, Piaget), and pioneers in early childhood education (Pestalozzi, Froebel); ""Overview of the Early Childhood Years"" indicates patterns of development (physical, motor, language, intellectual, social) and, with much citation of experts as well as general good sense, discusses salient issues (early education, spanking, fantasy play). The six age-span sections, however, are fragmentary, repetitious, and arbitrary--with some topics taken up time and again (not only basics like toilet training, but maybe's like moving), in particles. Each section is raggedly encyclopedic: The Loner, The Importance of Grandparents, Baby-sitters, Discipline, The Excessively Shy Child. . . Playroom Storage Facilities, Working with Wood, Phonograph Records (""The 37th Through 42nd Month of Life""). And no topic, however continuous, gets an integrated treatment. Most parents will find Penelope Leach's Your Baby and Child meatier, handier, and more genuinely helpful.