The petition must be filled out and signed in front of a Notary Public. You may need additional forms to change a child's name.Need a name change affidavit? Simplify the process with NewlyNamed's comprehensive kit. Signed and Notarized Letter explaining why a name change is needed. A Notarized Affidavit of Gender Error for a Person 17 Years of Age or Older (DOH-5303). You can file an application to change your legal name in any district court in Washington. The person requesting a name change is called the "petitioner.