Guardian  The guardian is responsible for the welfare and safe upbringing of an  infant. (under 18 years of age) at the time of your death. Parents who are making Mirror wills should name a guardian in their (both) wills in the event that they should die together, but appointment (or the responsibilities) of a guardian  (in most cases) will not take effect until the death of the surviving parent.  Guardians must be 18 or over. 

Did you know that if you die without naming a guardian, the state would, name one for you?...  AFTER they make this decision , COSTS would be incurred for doing it, payable from your estate.

If at the time of executing (making) your Last Will, you have any infants, (children under 18 years) then he or she should, in his, or her Last Will, appoint someone to act as a guardian for the infant, in the event that both parents should perish together prematurely.

Consideration must be given to appoint someone appropriate, who can possibly exercise the same love and care for the infant child, as you would have done yourself. Or at the very least give someone OF YOUR CHOICE a parental voice in the decisions of your infants child's future.

If a guardian is not appointed by you in your Last Will the state steps in and decides who will have parental responsibility for your child. The infant can be made a "ward of court". The state will do its best for the child, but why risk the unnecessary trauma this can cause. Make a Last Will and make YOUR wishes known. 

You could perhaps ask a close relative or Godparent to fill this important and responsible role.

A suitable executor can also act as guardian and vice versa. Great care and serious consideration should be given to whom this important role falls upon.  

This is a very important role and any ambiguity should be avoided when naming more than one.  Remember this guardian would only step in if both natural parents should die. Any surviving parent has guardianship in most cases.