This will depend on what vaccinations your child has had overseas and if you are able to provide valid records of their vaccination/s.
If the vaccination schedule of your home country differs greatly for the Australian Immunisation Schedule, or if valid records are not available for your child, then your healthcare practitioner or GP may recommend your child go through a catch-up schedule in order to be in line with the National Immunisation Program (NIP).
For more information, speak with your healthcare practitioner.