One of the matters that divorce lawyers are often asked to advise on is when clients with children fear that their child or children are going to be taken overseas without their permission. This can be especially problematic if they believe the absent parent plans to take the children overseas and not return to Australia.
Thankfully, there are laws and legal processes available that can prevent children from being taken overseas. However, that does not negate the possibility that the absent parent may take the risk and try to do so anyway, which would be illegal and risk criminal prosecution.
If you are a divorced parent and wish to take action to prevent your child from being taken out of the country, you should only do so for legitimate reasons, such as a fear they will not be returned. Simply trying to stop your ex-spouse from taking your children on an overseas vacation as some retribution or to spite them achieves nothing other than denying your children that experience.