My bike is an urban arrow, so one of the bigger two wheelers. ~7500€ new with all possible add-ons and a €150 annual insurance that covers the bike in full if ever stolen or damaged in an accident, so I also feel safe parking in rough areas with it.
60,000 people on a 4 year waiting list for on street bike parking:
https://www.standard.co.uk/news/london/london-cyclists-bike-...
Transport capacity is still great and the bigger version can seat two passengers, but the kids need to be old enough to sit and hold on themselves.
All of this stuff exists but the bike industry can't put 2 and 2 together.
Here is a link to a folding handlebar stem that is sometimes in stock: https://flatbike.com/product/thinstem/
On some brand I quickly googled[1], the bounding box that covers all of their models for electric bakfiet's size is 253cm x 95cm (with no individual bike being both that long and wide). Comparing them with a Fiat 500 and a RAM truck[2] (just for kicks), that bounding box is 1 meter shorter in both dimensions than the Fiat. And their classic model is 228cm x 63cm.
[1]: https://www.bakfiets.com/bestanden/documenten/618-22bakfiets...
[2]: https://www.carsized.com/en/cars/compare/abarth-500-2008-3-d...
I've read that in the Netherlands, they aren't as common as you'd expect, because kids just ride their own bikes almost as soon as they're able to walk, because school, sport etc is nearby and on a safe separated bike path network. While younger babies are carried in those little seats that mount on the handlebars or racks of regular bikes.
I don't think ability to be carried up stairs easily is a good criteria for the practicality of any bike though, or it rules out many ebikes too. Just need secure parking at the ground level.