I hesitated to comment on Sociables because my memory of them is very much off-topic relating as it does to bicycles (?) quadricycles (?) which were anything but lightweight. Sociables were very popular in holiday resorts in Britain in the thirties and forties, especially at post-war holiday camps. I am sure that many of our parents' photograph albums include dog-eared monochrome snaps of smiling Mum and grinning Dad on a sociable. I seem to recall somewhere for a five year old Stuart to sit.
A good idea now? I am not so sure. There was very little traffic then but now they would be a moving roadblock.
Stuart Tallack keeping a narrow profile in West Sussex