If you have children under the age of eighteen, you should designate a person or persons to be appointed guardian(s) over their person and property. Of course, if a surviving parent lives with the minor children (and has custody over them) he or she automatically continues to remain their sole guardian. This is true despite the fact that others may be named as the guardian in your estate planning documents. You should name at least one alternate guardian in case the primary guardian cannot serve or is not appointed by the court.