My own opinion is that riding in tight city roads in Europe would be difficult with a hex. These bikes are much nicer out on the open road with minimal stopping and starting. With the right team I am sure you could balance a hex and start and stop where only the captain put feet on the ground. I do this with our quad. However, if this only works with seasoned riders who don't lean way out unexpectedly. It also depends how heavy your kids are. You might want to read a bit from the blog of this family that decided with almost no significant preparation to ride a quint bike on a 7000 mile journey with small children:
http://www.pedouins.org/journey.html