Obviously you need to have passports for the children in order to take them overseas but if you do have the passports then it is important to understand the law.
While there are no Orders in place you can take the children out of the country BUT if the other party has commenced proceedings in Court and let’s say either no Orders have yet been made (you haven’t had your first court date yet) or the Orders are silent about going overseas then YOU CANNOT TAKE THE CHILDREN OUT OF THE COUNTRY. If you do remove the children from Australia after becoming aware that proceedings have been commenced in Family Court then you will be in Contempt of Court on which the punishment can range anywhere from a fine to imprisonment.
You also need to be aware that if you are contemplating trying to remove the children from Australia permanently then you risk a Hague Application being brought against you over in the country that you are relocating to (if the country is part of the Hague Convention). If you wish to relocate permanently with the children overseas then the appropriate course of action is to obtain written consent from the other parent or apply to the Court for an Order permitting you to relocate.