All children, when they are born, need to be taken care of. At first, we depend on our parents for the most basic things like food, sleep, and hygiene.
As we grow, we depend on our parents and family for education, expenses, and emotional support.
Of all species, humans have one of the longest dependence on our families and caregivers.
Obviously, a child is not in a position to take the right decisions for itself. Children do not have enough information and experience.
So, someone else takes decisions for us.
The person who is legally responsible for our conduct before we become adults, is called our legal guardian.
Usually, it is the parents of the child. But, in some special cases, it may be another relative or even someone appointed by the government.
After a certain age, a person is considered old enough to take decisions for themselves and to enter into legal agreements and contracts. Such a person is called an adult.
If A is your legal guardian, you are their ward.