I simply called the building authority and explained the situation. I emphasized that it is not about doing anything on the property before the completion of the development work, but that I just want to have the permit in hand for the Baukindergeld. You can find the thread about it --> .
Each federal state has its own building regulations, but I believe that in most building regulations it states that the prerequisite for granting a building permit is a so-called "secured development." One of the colleagues at the local building authority also mentioned this wording. However, I do not know exactly what this means. So far, I have found nothing clear that equates "secured development" with "completed development." If these are actually two different things, then I conclude that a development could in principle be considered secured before it is completed. Then granting the building permit would also be permissible according to building regulations. I can imagine that many authorities still wait for the completion of the development to be on the safe side, especially because this term "secured development" may not be that clear.
I believe the argument of Baukindergeld carries more weight than a fixed price guarantee. Municipalities always pride themselves on wanting to promote housing for families. And opposing that now contradicts the whole idea. Do you know any other builders in the development area who are also insisting on the building permit because of BKG? They should also inquire at the authority. If they say at the building authority that they cannot do that, demand a reason. How big is your town? Could you imagine going to the local press with this? Local elections are coming soon in NRW. Maybe with you as well?