How much house is in it?

Divorce is also a topic you should deal with when it comes to this type of financing. In our housing development (2 years old), 3 out of 20 builders are now going through a divorce. As mentioned, with 80% financing or less, you don't have to deal with such things, as both parties come out of the situation debt-free.

Proceed sensibly, buy an apartment, see how you manage the payments, and then plan the next step.

An apartment, which, if proper, is not available for less than ~200k and accordingly has high purchase incidental costs that will be lost with another purchase—if anything suitable is found at all? Plus the prepayment penalties in five figures for the early repayment of the loan for the apartment?

That’s not meant seriously, is it?

Yes, absolutely. It is certainly anything but easy and perhaps not actually feasible in every single case, but we’re not talking about parents in general here, rather about those who would be willing to restrict themselves accordingly for a home of their own.

Most take 2 years of parental leave, then work part-time for 6-12 months and have the second child shortly after, so the gap won’t be too big. Then the story repeats itself again. That way about 5 years go by during which one full-time income disappears.

The income doesn’t vanish completely, it’s just reduced. But as you yourself admitted, in the end it’s a matter of willingness. You just have to cut back on consumption, lower the repayment, or save up the shortfall in advance. In the case of the OP with almost 4,000 euros of disposable income, such “worries” are purely academic.

I just want to briefly point out that a desire to have children can sometimes become so strong that rational or financial considerations are put aside

I just want to quickly point out that the desire to have children can possibly become so strong that one puts rational or financial considerations aside

But that is more likely with people who have wanted children for a longer period. For example, I currently can’t imagine it at all. I finally found a job that I really enjoy, and I would very much like to work in it for some time before actually thinking about any potential desire to have children. And overall, I’m probably the one in my circle of acquaintances who doesn’t run after every stroller that passes by somewhere. Sure, it could change with my own children later on, but I really strongly doubt that I will suddenly feel such a big urge to pass on my genes that I would stop everything else for it. If someone were to present me with a fully restored 1969 Ford Mustang Fastback Mach I in Gulfstream Aqua, then holding back would be more difficult than with children. But that’s also my kryptonite...

Some people can only afford the house because they have to enter into short interest rate terms, otherwise it is not affordable. To me, that is gambling, especially when expenditure increases are foreseeable. A high level of debt and short interest rate terms, in my opinion, only work if high repayments are realistically possible and are actually made.

Spending hundreds of euros on insurance and not being satisfied with household budgets that show four-figure surpluses every month is, to me, the other extreme.

Both types will consider each other crazy.

And all of this is only because the loss of homeownership is somehow ingrained in people's minds as the ultimate disaster. Social decline, right before the end of the world. As if one could no longer exist without it (or would be worthless, maybe more like that?).
My wife and I have a large income gap. If I no longer work, there is no house anymore. It's that simple.

I just want to briefly point out that an Eigenheimwunsch can possibly become so strong that one puts rational or financial considerations aside