Language
This period runs from birth through approximately age 6. During this period the child is extremely sensitive to vocal sounds and to movements of the vocal apparatus. Deprivation of language stimuli during this period can lead to severe language deficits. Without stimulation, the synapses of Broca's area and related language-processing areas of the brain will literally waste away.
Order
The sensitive period for order operates most actively between roughly the ages of one and three years. In this period, the child is organizing a mental schema for the world. In order for firm conclusions to be drawn about the world, the child must be able to impose an order on it - one which can be relied on as constant to observation. If this need is not met, the child's ability to reason and learn will be precarious, since she may not be able to consider her conclusions reliable.
Sensory Refinement
This period lasts from birth to about age 4. A child takes in information about the world through his senses. As the brain develops, it becomes able to discriminate between relevant and irrelevant sensory stimuli. The most efficient way to accomplish this is for the brain to pay attention to all sensory stimuli. The most repetitive (and therefore most important) of these will strengthen neural pathways, while the less common, although initially detected, will not provide enough brain activity to develop sensitivity to them. By age 4 or so, the brain has finished its "decision-making" about which stimuli are relevant, and worth attending to. Other stimuli will be ignored. This period, then, is important for helping the child attend to differences in sensory stimuli, which in turn can lead to a greater ability to impose a mental order on his environment.
Refinement of Motor Skills
This period encompasses the time between roughly 18 months and 4 years of age. By the beginning of this period, the child's gross motor skills are generally rather well developed. At this point, the continuing development of the cerebellum and motor cortex allow the child to increase her fine motor skills. Activity on the part of the child which focuses on fine muscle control (writing with a pencil, picking up and setting down small objects, and so on) will allow the child's muscular skills to develop to a quite advanced level. After this period, the neural control of the muscles is relatively fixed, and improvement in fine motor skills comes only with considerable effort.
Sensitivity to Small Objects
This period, between roughly 18 and 30 months, might be viewed as a consequence of the overlapping of the previous two. As a consequence of the child's attention to sensory stimuli, combined with an interest in activities requiring fine motor coordination, the child takes an interest in observing and manipulating very small objects, which present a greater challenge to the senses and coordination than large ones.
Social Behavior
From about 2½ through 6 years, the child, having become relatively stable in his physical and emotional environment, begins to attend to the social environment. During this time, in an attempt to order this aspect of her surroundings, the child attends closely to the observed and expected behavior of individuals in a group. This attention and ordering will allow her to move through the social environment in a safe and acceptable way. Children who are, for whatever reason, largely or entirely deprived of social interaction during this period will be less socially confident and perhaps more uncomfortable around others, a feeling which may take quite a bit of effort to overcome.