Further leave to remain

[nottsboy]

Hi
I am applying for my partner visa extension. Homeoffice has introduced new online application system now.
I have two kids they are british as myself but my wife is not ready to apply for indefinite leave.
While applying for her extension the new requirement for the visa at one place asking

Birth certificate of both of Miss A.K parents.

Miss A.K is my daughter who i mentioned because they were asking. And the same for the son

They never asked me my birth certificate or my partner before. We do have our ID cards and passports but unfortunately birth certificates are not present.

what should we do to at this very moment.
Thanks.