Traditionally families often just had one bedroom for children. That's what things like bunkbeds are for.
"Just stop preferring that"? Good luck enforcing that.
I guess this will work for something like 10-20%? Maybe? (Speaking from a very german cultural background)
Even then, it would not solve any problems here, really.
On one hand, all of this is understandable, but on the other hand these policies do indeed raise the cost of having children.
Fuck that.