Last week I picked up an Alleycat bike extension that is kind of a tandem/trailer conversion. One benefit of this is that it allows a child to ride in tandem behind their parent. greater distances can be travelled because the child doesn't have to work hard to keep up with an adult. They can pedal as much as they like or simply free wheel it as Mum or Dad do the pedalling. I won't be able to use it for a couple of years but have already found a grateful home for it until my daughter is old enough to ride.