Wait with the building application because of the child construction allowance

Yes, that's right, but I find the order of building the nest first and then having children more sensible and thus also eligible for funding. This way, you can first analyze your finances with the house. Of course, I accept it as it is, but it would have simply been nice. Unfortunately, we did not receive a single funding for our entire construction. As I said, I just find it a shame when you see that the neighbor with the new Audi gets the funding and we with our 10-year-old Opel are not eligible for funding. They could have also considered planned children up to 2 years after moving in. And yes, I also know that anyone who makes their financing dependent on the child construction grant should not build. (Here the frustration wrote along)

That's exactly how we feel: homeowner allowance in Bavaria doesn't apply because it was already at the notary in 11.2017, child building allowance also doesn't apply because our child will only arrive in the next few days. Move-in was 1.2019. Everything missed. The neighbor already had 3 children at the notary appointment and signed there in January 18. That makes 46,000 in funding, and he deserves it too.

a correct but I find the order of first building a nest and then having children more sensible and thus also eligible for funding.

This is not feasible within the scope of funding.
The funding goal is to bring families into homeownership. Children are part of the definition of family.

The consequence would then be an obligation to have children within period X. That would probably be incompatible with the Basic Law.

Although we ourselves receive it, I consider the child construction grant to be nonsense. CSU clientele politics, especially noticeable in the high income limit.
On the other hand, I am glad that the child construction grant is relatively unbureaucratic. It is always bad when large shares of x billion in funding flow into administrative costs just to ensure fairness for everyone or to eliminate any potential for abuse.

But why get annoyed.
If I had built two years later, I would have benefited from an even lower interest rate level and would save five-figure amounts in interest.
I also had to build KFW 55, but didn't use the €5,000 funding because the KFW loan itself was more expensive than the bank loan. Today there is €18k for that.
However, the land has already increased in value by €20k and presumably today's new build of this building would also be more expensive than "back then".

The consequence would then be an obligation to have children within period X. That would probably be incompatible with the Basic Law.

Well, granting Baukindergeld not only for children present at the time of moving in but also for up to two years after moving in for children born until then would be absolutely compatible.

Well, granting Baukindergeld not only for children present at the time of moving in but also for children born up to two years after moving in would be absolutely acceptable.

Why should one subsidize a house that has already been built retroactively?

because this proves that the nest has also been created for one's children.

Especially when, like us, one comes from a two-room apartment