OK. You need to tick 3c and 3d on page 5, as you have ticked previous MIAM attendance as well as urgency.
Section 4 you leave blank as you are claiming exemption. So you do not need the mediator to sign off.
You need to put more details in section 5b - about why you are making the application, the agreement in mediation etc.
You should attach to the application the mediation agreement and the messages where you are told that the children will not be made available.
I would also not say that you owe her money, I would say "due to a dispute over a small amount of money that the Respondent claims the Applicant owes her, the Respondent has indicated she will now not honour the mediation agreement made on 12 July 2019 and refuses to a) provide the Applicant with the children's passports and b) confirm that she will make the children available for the planned holiday. As mediation is not legally binding, the Applicant has no choice but to apply to court for an order permitting travel."
Section 6 is just about why the application is urgent. So that's the dates etc - the rest goes in section 5b as background.
So you are almost there, just a few tweaks to make.