I have two children (ages almost 5 and 2) and have used my Xtracycle a bunch this past summer carrying them and their stuff to daycare and to the park. Though besides hauling kids, I have used the Xtracycle to commute to work and go grocery shopping. I've also made a couple of trips to Target, so you see the utility of such a bike is more than just hauling kids. Do you see yourself riding to places that you would normally have driven your car? You mentioned a triple tandem, that would get your kids involved in the pedaling which is a great alternative but quite a different experience. I probably wouldn't get rid of the minivan as well as having access to a vehicle that can hold all of your is a great asset. I see you intentionally did not mention an Xtracycle and in your shoes that is a wise choice. I love mine, but I would not want to haul much more than my smaller kids and their things as you start experiencing the frame wiggle that is annoying. I agree, get a purpose built cargo frame for your family.