A Guardian is the person(s) that you nominate to take responsibility for your minor children in the event that both parents are no longer living. This is a very important role and one that requires serious thought.
It is recommended that you discuss the appointment of a guardian with them prior to completing your Will.
In most cases a surviving natural parent assumes guardianship of minor children. However, if there is a dispute, the court takes into account whether someone has been appointed as a guardian in the Will.