For the early years and utilizing a tandem with my children, I installed "ape hanger" hanger handlebars (what you would see on a 1970's Schwinn) and fashioned stirrups to go across the top tube. At the least, turn the drop handle bars over. It will place them closer to the rear seat.
I've pulled a trailer with this set-up, toured Florida, Kentucky, and Denver,Colorado. Be sure to remove the pedals so the kids feet don't catch on them.
They will have much more fun riding and looking around than attempting to pedal. The pedals will be too long for them anyway.