growing pains

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun plural Pains in the limbs and joints of children or adolescents, often attributed to rapid growth but arising from various unrelated causes.
• noun plural Emotional difficulties that occur during adolescence.
• noun plural Problems that arise in the initiation or enlargement of an enterprise.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun generalized pains in the limbs or joints of adolescents (from many causes)
• noun emotional or social problems associated with adolescence
• noun by extension difficulties that arise in the early stages of any project

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun pain in muscles or joints sometimes experienced by children and often attributed to rapid growth
• noun problems that arise in enlarging an enterprise (especially in the early stages)
• noun emotional distress arising during adolescence