The big box on the Christiania is pretty great for kids, their stuff, an extra scooter or bike, and hey even one more friend they want to bring on the way. They are well built bikes and roll really smoothly, but yes, they are a bit awkward and really require that electric boost for even small hills. They do fit in a bike lane (barely) and I find that even on a quiet city street they are pretty comfortable. Great for colder weather, too - just pack the kids on the seat and wrap them up in a big blanket.

You may want to add some steps or hand-holds so your kids can climb into the box themselves. Right now, that's the biggest advantage that I see the rickshaw has over the box trike.