The High Court has jurisdiction to deal with child abduction; the Hague Convention largely governs this issue.
If a child is taken from his/her habitual place of residence into another State/Country without the permission of the custodial parent, a Hague Convention application may be made. Both countries involved must be signatories to the Hague Convention.
Such applications should be made quickly; therefore it is very important that you consult a specialist at the very earliest opportunity. Delay can defeat an application, because the longer a child is in a new place, the more reluctant a court will be to return the child to his/her habitual place of residence.
In general the children should be returned to their habitual place of residence, unless there are grave risks to the child in being so returned.