I went and tried the Bakfiets Cargobike, both the standard and long sizes and i have to say we loved them. It is a two wheeler and feels like a normal bike would feel to ride. The long box is the one we will choose, you can fit up to 4 kids in, or two kids with all their bags and kit, eg. small bikes, childrens toys etc as well. The small version is still pretty roomy too.
The ride was smooth, brakes excellent, other road users smiled, gave us lots of space, and the nike was nifty to manoever. Very impressed with its handling.
There was a bike rack with integral bungee cords, 8 gears, puncture reistant tyres... you can tell i'm hooked can't you!!!
We saw a lady in Richmond, who is an agent and does free demo's of this bike. It's a long story why we didn't actually see any other bikes, but it didn't matter anyway, as we know we'll buy the Bakfiets Cargobike Long.
I could say a lot more about it, but I will say you can wheel it easily backwards up a kerb onto the pavement if you need to. It has an integral lock so it is easy to park up outside a supermarket safely when shopping for example.
Any more questions please ask, i'll try and answer. Just need to see if we have the cash to buy asap, may need to wait until next month.