Children born in UK

I have a South African Passport & Citizenship, & have lived in the UK for 18 years now, being married to my wife who is Danish (hence EU Passport). The question is do our children who were born in the UK, who are now 11 and 15 years old, qualify for British Citizenship and Passport automatically? They both currently hold Danish passports. If they do, how do I go about getting this done, please (forms, etc)? Thank you

Do you hold ILR? Was it obtained before the children were born?

Alternatively, have your wife hold ILR which was obtained before the children were born? Or has she been working for continuous 5 years in the UK?