A novelist invented the postbox
Before the 1850s, posting a letter in Britain meant carrying it to a post office while the post office happened to be open. The man who changed that was Anthony Trollope — better known now for writing dozens of Victorian novels — who worked for the Post Office and was sent to the Channel Islands to sort out the mail.
His suggestion was a locked iron box on a street corner that a POSTMAN could empty on his round. The first ones appeared in Jersey, the idea spread across Britain within a decade, and Trollope kept writing his novels before breakfast and going to work afterwards.
The helpers you stop noticing
Some are unmissable: the POLICE officer, the FIREFIGHTER, the DOCTOR. Others do the work while the street is empty. Bin crews start before six in the morning. The CLEANER arrives before the office opens and the JANITOR locks up long after everyone has left. The GARDENER is the reason the park is usable at all.
A good question to ask a child is who has already helped them today, before breakfast. The honest answer usually includes several people they have never laid eyes on.
Paid for by everybody
Most of these jobs are paid for collectively rather than by the person being helped. Nobody hands the FIREFIGHTER a card at the door. The LIBRARIAN does not charge for the books. The crossing WARDEN is not paid by the children crossing the road.
That is easy to explain plainly, and it is where a good deal of early citizenship begins: everybody puts something into a shared pot, and the pot pays for the things that anyone might need one day and nobody could afford alone.
The lollipop is only seventy years old
School crossing patrols started in Britain in 1953, and the round sign on a pole followed shortly afterwards. It is a circle because it has to be read from the front by a driver and from behind by a child at the same moment, and it is enormous because it has to work in rain, at dusk, through a windscreen.
The CROSSING patrol is one of those jobs defined almost entirely by standing in the right place at the right time. It is also, reliably, the first job in the neighbourhood that small children learn the name of. The British version wears a white coat and carries a sign reading 'Stop, Children', which generations of schoolchildren have cheerfully chosen to misread as an instruction.
Where a first ambition comes from
Ask a five-year-old what they would like to be and the answer is nearly always a job they can actually see: a VET, a TEACHER, a BAKER, a POLICE officer. No child says actuary or logistics planner, because nobody has ever pointed one out.
That is a decent argument for mentioning the invisible jobs as well as the visible ones. It is also a reason to make a fuss of the visible ones, because a child who grasps that a NEIGHBOUR lending a ladder and a VOLUNTEER giving up a Saturday are doing something valuable has understood most of what this topic is for.