Thanks for your input! I don't want to have them running loose on their own bikes quite yet on busy streets etc.- around the block, behind the house for fun, sure, but not for everything.

I am now checking out tandems. Schwinn makes some reasonably priced cruiser tandems that with a couple of baskets could haul a lot of stuff.

So maybe what I need to do is get a nice simple used solo bike for me when I'm not in kid-hauling mode and then the tandem decked out with baskets and an extra seat stuck somewhere on there for when we're doing the school commute, etc. Having at least one of them helping peddle would be great on a couple different levels. And as they grow I think it would be fun to do tandem rides around as well.

Your points about the "tipability" of the trikes are interesting to me. I just assumed that they would be rock solid... I am looking at the Twin Tri-Rider tandem trike but that ain't cheap and it looks like it could be real work to get that thing moving! I will look up reviews.

Thanks again!

Edited to add - my kids aren't anywhere near 60 and 90 pounds but I know at least the Yuba Mundo is rated to carry 400 pounds so I think if we went towards the utility bike route it should be possible to carry it off. Now hubby is aghast at the idea of our two girls on the back rack of a bike - even tricked out with safety measures. Does not consider it safe at all.