If the children are being taken to live outside the UK you can take action to have them returned so that a Scottish court can decide whether this removal should be allowed.  Consult a lawyer who has experience in such cases and see the Scottish Government guidance.  If the children have been taken to a country which is part of the Hague Convention this process will be easier.  You can also seek support from the Central Authority for Scotland and Reunite.

If the children are simply being taken for a holiday, you should have been asked to give your agreement if you have parental rights and responsibilities.  Rather than making this into a conflict, we suggest that you should agree to holiday trips and offer to provide the other parent with a letter giving your authority in case there is any problem when leaving the UK.  In return you can ask for details of the trip.  Trying to stop a holiday trip won’t be popular with the children, and if you go to court to try and stop it you may find that a sheriff will allow the trip and you risk being accused of controlling behaviour.