Are there any court orders in place, that cover this?
Do you have a parenting plan in place that covers this?
Have you and your ex been to court, or currently going through the Family Law Court system?
Would the child be flying on an Australian Passport?
To answer your question without knowing the above, I will say this, if there are no court orders in place regarding living and visiting arrangements of your child, then yes technically you are free make arrangements and head off overseas. If there is court orders in place regarding visitations, then no, as you will need to come to an agreement with your ex regarding, how you plan on giving him extra visiting time to make up for the time he doesn't have with the child whilst you are away.
Cheers
