A power of attorney is a document in which you, the principal, name another person, an agent or attorney-in-fact to act in matters on your behalf. Many military personnel create POAs before deploying overseas in case something happens that needs immediate attention or in case they become incapacitated. Incapacity is probably the most common reason people need POAs. A limited POA lets someone act in a specific situation. For example, you want your son to help you sell your home or help you move into a care facility. Upon completion of the task, the POA ends.
You might want to grant a financial power of attorney to one child to help you manage your stock and investment accounts. You could also divvy up responsibilities among your children with specific POAs. One person could manage day-to-day bills while another has access to long-term accounts.