Adrian, @Mercian, is right re. the 'plaque fiscal', annually changing the insert for that years 'tax' was what happened.
They often have the then owners name and address stamped on. I know people who have been able to trace their machines early history using these.
Definitely looks very 1920's to me,; that childs seat is a gorgeous little period accessory.
The seats may have manufacturers names/model numbers on them also.
Looks very complete and very original.
A really nice find!!!