The newly found images, by Edward Detmold [1883-1957] and Charles Maurice Detmold [1883-1908], were published when they were just 20.
They had gone unrecognised in London for decades.
The owners, who have not been named, said: “These drawings were never treated as ‘important’ works in our family – they were simply part of our home.
“Finding out that they restore a missing piece of the visual history of Kipling’s The Jungle Book, has been completely unexpected.”
The first of the two watercolours, by Edward Detmold, depicts Mowgli and Bagheera.
The second, The Cold Lairs, is by Maurice Detmold and shows monkeys in the ruined city of the Bandar-log.