I will echo what the others have written. I use my 30 year old MTB bike converter to a 'hybrid' set up to haul the kids either in a child seat, a Thule Chariot, or both. I don't know if it's just me, but using my beater bike for this makes it a lot less stressful than if I was using one of my 'nice' bikes. Will the child seat frame attachment leave scratches on the frame? I don't care. And my bike has fallen over and scratched more than a few times when I am putzing around with the kids in the Chariot.
One last advantage: when we go somewhere and have to lock up the bike and wagon, I only worry about the wagon. The bike itself is functional, but largely worthless to a thief (scratched up frame no decals, etc.).