There is no law that says you cant discipline them physically. But if you do then depending on what the police are told and what they see you may be charged with assault.
A slap on the backside would not be assault but across the face you will have issues.
You have to explain what happened and what you did.
Here is some information on what the law says in australia
If your children keep reporting you they risk being taken away and they should be made aware of this.
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