What you can't see from the picture is that this is a folding tandem specially designed to take a kid on the back- the Bike Friday Family Traveller
I can't actually tell how it folds from the photos, but it claims to fit in a suitcase.
I don't know if it would be simple enough to fold on a daily basis, but if it were, it could be a good solution for someone looking for a kid bike with a tiny apartment. Longtails aren't much worse than a normal bike to store, but Bakfiets and cargo bikes are not easy to fit in a city apartment.
It claims that the stoker can be from 3'6" to 6'3" so it would be useful for a long time.
This is clearly their daily child transport bike, as I see the father riding with the empty bike (presumably after drop off) quite often. I think it's an interesting option that you don't often see for kid transport.