You can leave anyone out of your will, unless it is your spouse or your child. Many laws have been enacted to protect spouses and minor children. Be sure to read the "Marriage and Wills" section in the "Wills Education Center" for more information.
If you wish to disinherit one of your children or give one child less than another, you should clearly state that intention in your will and the reasons why. The law has special protections for minor children. For instance, they are protected from the loss of the family home. You cannot give your home to someone else if your child will have to move from the home.