Choosing a Surname: Legal Advice for Parents

Questioner

My girlfriend and I had a daughter last year. If it were a boy, we wanted to give her my last name. If it were a girl, we wanted to give her my girlfriend's last name. The reason for this lies in a generations-long family tradition in naming and on the other hand the extinction of a last name. So our daughter bears my girlfriend's last name. We are now expecting a second child that we want to give my last name, regardless of whether it is a boy or a girl. After some research it appears that this is not allowed; brothers and sisters of the same biological parents must have the same last name. However, there seems to be a possibility to get this done. I have not officially acknowledged our first child yet. We can give the second child my last name because I acknowledge it in time. Of course I want to acknowledge our first child, but we can do this after the birth of the second child. She will then keep her mother's last name. My question is as follows; the above trick is not in the 'spirit of the law'. 1) Is our reasoning above correct & can we still achieve this? 2) Can the legislator later claim that we have found a loophole in the law and have deliberately 'misused' it to act against the spirit of the law? We do not find the 'spirit of the law' of this time and find our choice of naming important. However, if (question 2) the legislator forces us at a later time to change one of the two surnames, this is an unpleasant and expensive consequence. I hope you can provide clarity on the above. Thank you in advance.

Lawyer

A nice reasoning, but unfortunately. As soon as you acknowledge your daughter, the registrar will see that you already have another child - acknowledge - in the same relationship. The surname of that child is leading and will then also become the surname of your daughter.