Gather the necessary materials. You will need the full birth certificate with the names of both parents as well as proof of citizenship for the Australian parent or parents. Passports, permanent residency documents or citizenship documents will suffice. You will need four passport photos measuring between 35mm and 40mm wide and 45mm and 50mm deep. For a child born overseas, you will need to provide an Australian Citizenship Certificate. Any documents that are not in English must be accompanied by a certified translation.
Find a guarantor to sign the back of the photos. The guarantor should not be related to the child and should not live at the same address. The guarantor can not be the biological parent's same-sex partner. The guarantor must have known the infant since birth or at least for 12 months, and the guarantor must possess a valid passport. Have the guarantor write "This is a true photo of (child's name)" and sign the back of three of the photos.
Fill in the application form online here: https://www.passports.gov.au/Web/Forms/Passport/Child/ChildPassport_1.aspx. You will need to consult your documents and enter information about your guarantor.
Set up an interview to lodge the application with the Australia Post. Not all post offices accept passports and appointments may be required. Call the Australia Post (131 318) to find the nearest acceptance facility. If you are residing overseas, contact the nearest consulate or embassy for information about where to lodge the application.
Lodge the application, along with all supporting documents and the passport photos, with the Australia Post. You will need to bring photo identification and proof of name, signature and residential address to the interview. Two passport photos will be handed in with the application, and the two others will be presented at the interview. You must pay the application fee ($104 for a standard 32-page child's passport) at the time of application.