Good Afternoon Rob,
If he wants to be nasty he can file an application with the courts and request that she not be permitted to take the children to QLD.
He can seek orders that the children spend time with him over the christmas period and it would make it difficult for you her to bring them to you.
It is not an easy matter to resolve.
Is she prepared to try and reach an agreement with him about the children? It is always best to have an agreement.
How long does she want to bring them up for? What does she intend to do about the children spending time with their father over this period.
The usual orders are that christmas day is split. One parent has the children form christmas eve to 3 pm Christmas day and the other then has the children from 3 pm Christmas day till evening on boxing day.
What is she planning to do?
If he does take her to court, the court will not permit her to bring them up for Christmas and will say she can bring them up later.
If he does nothing then she can take them but he can file an application fro them to be returned and it will not look favourably on her.