By definition, a legal guardian is a person appointed by the court who holds full legal responsibility for the care of an incapacitated person or minor child, and is also responsible for managing their affairs: medical, legal, financial and otherwise.
Simply put in relation to a child, it is the role of a legal guardian to help protect a child, provide for their daily care, and manage any financial assets the child might have.
While parents are considered the legal guardians of their children until they turn 18, there are circumstances that make it beneficial for parents of physically or mentally disabled children to petition to retain legal guardianship once those children turn 18.
Disabled or not, once a child turns 18, they are held legally responsible for all of their actions. They can enter into contracts, sign purchase agreements, and be held accountable for any expenses incurred. Petitioning to remain the legal guardian of disabled children protects them from individuals wishing to take advantage through fraudulent interactions.
A legal guardianship over a non-disabled child should not be confused with a formal adoption. A legal guardian only retains responsibility for a child until he/she turns 18, unless the court sees fit to dismiss the legal guardian sooner. A full legal adoption actually establishes a parent/child relationship that remains in effect for life.
A legal guardianship is also necessary to complete international adoptions from some countries. India for instance, makes no provision in its laws for foreigners to adopt Indian children. Therefore it is necessary for the prospective adoptive parents to gain legal guardianship over the child in order to bring him/her back to the United States (or their country of residence) where the formal adoption procedure will take place.
The role of a legal guardian is not one to be entered into lightly. Be sure you are fully informed about all the responsibilities involved before you accept the position.