Chapter5: Physical Development in Infancy & Toddlerhood
GURE 5.21
Acting on the environment plays a major role in perceptual differentiation
Crawling and walking change the way babies perceive a sloping surface. The newly crawling infant on the left plunges headlong down the slope. He has not yet learned that it affords the possibility of falling. The toddler on the right, who has been walking for more than a month, approaches the slope cautiously. Experience in trying to remain upright but frequently tumbling over has made him more aware of the consequences of his movements. He perceives the incline differently than he did at a younger age.
Summary
Body Growth
Describe major changes in body size, proportions, muscle–fat makeup, and skeletal growth over the first two years.
■ Height and weight gains are greater during the first two years than at any other time after birth. Body fat is laid down quickly during the first nine months, whereas muscle development is slow and gradual. Parts of the body grow at different rates, following the cephalocaudal and proximodistal trends, resulting in changing body proportions.
■ Skeletal age, a measure based on the number of epiphyses and the extent to which they are fused, is the best way to estimate the child’s overall physical maturity. At birth, the bones of an infant’s skull are separated by six gaps, or fontanels, which permit the skull to expand as the brain grows.

Brain Development
Describe brain development during infancy and toddlerhood, current methods of measuring brain functioning, and appropriate stimulation to support the brain’s potential.
■ Early in development, the brain grows faster than any other organ of the body. Once neurons are in place, they rapidly form synapses and release neurotransmitters, which cross synapses to send messages to other neurons. During the peak period of synaptic growth in