By arguing before the Court in Vancouver about the substantive issue you attorned to the jurisdiction of the court.
The only thing you could have done with that court is to take the position that the court did not have jurisdiction.
But actually if the children live in Vancouver now and this is their habitual place of residence the Vancouver court does have jurisdiction over them and so does have jurisdiction over child support.
So even if you had not made this error the court would still have jurisdiction and the court in the UK should not agree to take jurisdiction any more.
At the same time that should not matter as you certainly have the right to a full hearing after financial disclosure on both your parts and then the order will be made.
And the order will be based on the Federal Child Support Guidelines and on your income so there will not be any uncertainty as to what you need to pay going forward.
You can use this online support calculator to work out what you will have to pay:
Does that help clarify the law?
Please feel free to post back with any follow-up questions you may have. If you don't have any then I hope I have earned a 5 star rating but if you don't feel that I have please don't hesitate to reply back and let me know what more I can do to assist you. Finally, please know that even after you rate me I will be here for you and you can ask follow-up questions if you think of them later on at no further charge of course.