The apartments became bigger, over 100 square meters or 1000 square feet’s.

And consequently more expensive? I mean raising children in the city is usually a question of paying a lot of money or living three to a bed.

This does not sound like a public policy solution, but parents paid more for bigger flats

In Norway until recently even with 2 kinds the assumption was that the family needs to move to a suburb either to own house or to rekkehus, a terraced house that shares walls when few others (hills and mountains made that a good fit). This was much more expensive than an apartment in the city.

What newer apartment blocks brought was an option to stay in the city. Surely a 3-bedroom apartment with a big living room and a kitchen costs more, but prices are comparable with own houses in far away suburbs. That gives an option to stay with kids if not in the city center then at least within a short ride from it in public transport.