My ex-husband and childrens'' father is American. Children have British and American birth certificates. I have a residence order for the children.
I was informed by Passport control and from reading the residence order that when my ex takes the children out of the country for holidays, he must have a letter of permission from me to allow him to go.
I was also told that he can apply for British passports for the children in his own right.
I have now been told by passport office that if a father has the same surname (which he has) that border control have no need for such a letter and will not have any concerns.
What steps, if any can I take to allow certain holidays for him with the children but not allow travel to the USA?
Why do you want to prevent travel to USA ? You would need to apply for a PSO (Prohibitive Steps Order) however I would have thought it wouldn''t be easy to defeat as I suspect your ex could argue he would like to take the children to his country to meet their extended family there. The USA are signed up to the Hague convention so if your ex attempted to abduct your children and take them to the USA the authorities there would take action to return them.
Your ex requires your consent or permission from the courts to take the children abroad. However unless there is evidence of a flight risk the courts are unlikely to prevent him taking the children abroad on holiday. International Child Abduction is a criminal offence. The US is a signatory to the Hague Convention on child abduction so if your ex kept the children abroad they should be returned to the jurisdiction of the courts in the UK where they habitually live.
The charity Reunite has some resources about preventing international child abduction on there website you might find useful.