When our family lived in France, 1988-89, we only had one car, and my wife often needed it to get to work. That left me to pick the kids up from school in the afternoon. The photo above shows the rig I used to do this. I would attach my daughter's Cinelli BMX 3-speed to the back of my kidback tandem with a couple of toe straps. This way I could ride down to their school carrying my daughter's bike, then we could ride back together.

My daughter, 8 years old, would ride her Cinelli, and her brother, 6 years old, would ride the back of the kidback tandem.

This would not have worked if I didn't have a freewheeling "bottom bracket" for the stoker position of the tandem, as the left pedal would have bumped into the bike strapped on in back.