Hi Steve!
My, what a fascinating "problem" to contemplate even for a non-deliberately childless person like myself!
When I was a wee lad, I rode with my father on his 1938 Hercules coaster brake bike in an ancient setup very much like Rachel's Option 3 (
http://www.amazon.co.uk/WeeRide-Deluxe-Child-Baby-Bike/dp/B001F6FN2S/ref=pd_sim_sbs_by_3 ). The current model looks ever so much more refined (and likely safer as well).
What we both liked most about it was the way the parent-rider's arms formed a protective shield for the little passenger's head in the event of a fall. Also, the child is up front where they can be seen and conversation is easy. As wee passenger, one of my fondest memories relate to thinking I was able to steer. Good times. I did see a few of these when I was in Belgium; the rear-mounted seats were overwhelmingly more common in The Netherlands by my casual observation.
I almost think this is the setup I'd prefer if I were to carry smallish children, but my preference is likely colored by happy memories.
I do think Andy (ajbenie) makes a couple very key points about weight up front and knee clearance with larger children. As I recall, I maxed out of our version midway in my third year, though that doesn't quit square with the ability to log happy memories at such a young age....
I do have visions of what a 40lb max weight might do to the unbutted portions of a top tube, but I see the illustration shows the seat mounted on what appears to be an alternative...spar?...spanning the gap in what is essentially a step-through frame, so tube-damage concerns are likely unfounded. As for paint, you could always wrap the top tube with vinyl tape.
WRT to the Cheriot trailer and Gil's comment about Utopian hand-holding while towing the lot...well, this is a really effective and appealing sales video!
Please let us know what design you end up choosing, Steve, and how it works for you in practice.
All the best,
Dan.
