The idea behind the cages was patented in America in 1922 as a means to help parents living in cities who didn't have much space.

The benefits were said to be fresh air for the child, room to play with toys and another place for children to sleep.

The patent was filed in 1922 by Emma Read, from Washington, and was granted the following year.

According to The Northern Star, the description of the patent, said: 'It is well known that a great many difficulties rise in raising, and properly housing babies and small children in crowded cities, that is to say from the health viewpoint.

'With these facts in view, it is the purpose of this invention to provide an article of manufacture for babies and young children, to be suspended upon the exterior of a building adjacent an open window, wherein the baby or young child may be placed.'