One of the main reasons to get a good Will signed is to have guardians of your minor children appointed. This is accomplished by including Will language like this:
Guardian Provisions
If my Spouse fails to survive me, or if he/she dies after my death without having appointed a testamentary guardian for any minor child of mine, I appoint ____________________ to be Guardian of the persons and estates of those of my Children who are under the age of legal majority at the time of my death, without requirement of bond or other security.
Otherwise, the Court will be deciding who gets to take care of your minor children.