Explain how inappropriate stimulation—either too little or too much—can impair cognitive and emotional development in the early years. (1 point)

Both under and over stimulation can greatly affect childhood development. 

For cognitive development :

Brain develops in such a way that its neural pathways become resilient  because of its need to respond to activities in his environment. In the absence of stimulation, the brain cells (neurons) degenerate and die. Excessive stimulation, on the other hand, can hinder progress because in the early years, their nervous system is still immature and is not able to process too much stimuli at one time. 
For emotional development : 
Absence of parental nurturance or excess thereof can affect early childhood in terms of their ability to keep calm, or balancing desires. Stimulation in this case is warmth or love and too much or lack of it may lay unstable foundations that will affect their life later on. (i.e. ability to handle stress, trauma)