Pervasive Development Disorders
(PPDs)

The term "pervasive development disorders," also called PDDs, refers to a group of conditions that involve delays in the development of many basic skills, most notably the ability to socialize with others, to communicate, and to use imagination. Children with these conditions often are confused in their thinking and generally have problems understanding the world around them.

Because these conditions typically are identified in children around 3 years of age -- a critical period in a child's development -- they are called development disorders. Although the condition begins far earlier than 3 years of age, parents often do not notice a problem until the child is a toddler who is not walking, talking, or developing as well as other children of the same age.

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Source: MedicineNet.com
http://www.medicinenet.com/pervasive_development_disorders/article.htm