I tow my two kids in a trailer on various bikes and have not had any problems. The seats are cool if you are not traveling too far as my kids (1 1/2 and 3 1/2) tend to fall asleep while on longish trips. I don't know how comfortable a kid can sleep while hanging to side of a bike on a seat, but my kids have done it and the wife doesn't like it. I would go with a trailer if your kids are small. It also offers a bit of protection from the elements as opposed to riding in a seat.