Feasible financing for couples with future children?

A house costs money, especially as it gets older. And who wants to have to sell their house in old age for financial reasons?

However, one should always keep in mind that an apartment is, in 99% of cases, significantly more expensive than the house in old age. There is a reason why retirees who own property are generally much better off than their counterparts who rent (even if both families earned the same before).
Selling a house in old age usually means that with normal real estate, you can either buy a smaller and cheaper apartment (then the argument of retirement provision applies again) or you have to pay higher rent (even if this is somewhat subsidized by the proceeds from the house sale).

what I was getting at: one should advise a young, potential homebuilder against seeing the house as the sole retirement provision, but rather as one possible pillar among several, so as not to have to sell it eventually due to lack of liquidity.

in order not to have to sell at some point because there is no liquidity available.

But that applies per se to all people. I say the same to tenants, liquidity must be available, otherwise you end up on the street if your pension no longer provides enough money. And tenants usually need even more liquidity.
What could be better than not having to pay rent (or almost none) in old age. The incidental costs for the house are not much different than for the apartment.
In this respect, I have to disagree with you.

Yes, the house as the sole retirement provision is a powerful asset that can be leveraged. Very powerful.