Paraphrasing of the third stanza of the poem
Surely Shakespeare is wicked, the map a bad example
According to the poet, Shakespeare's picture is of no use to these children. It is the symbol of high quality literature but they are struggling even for basic facilities. The map is also a bad example for them as it is the symbol of world for them. Their world is limited to their windows only.
With Ships and sun and love tempting them to steal
The pictures of ships, sun and love tempt (attract) these children. They also want to live that life.
For lives that slyly turn in these cramped holes
From fog to endless night.
According to the poet, slum children want to live the life depicted in pictures. But their life is limited to their cramped holes (uncomfortable small homes) . A very poor life has entered into their homes stealthily which starts at fog and end also at night. Fog and endless night both are the symbols of being unclear and clueless. Fog and endless night are two poles of their life. We can say there is no clarity about their future.
On their slag heap, these children
Wear skins peeped through by bones and spectacles of steel
With mended glass, like bottle bits on stones
According to the poet, these children live in the houses which are made of slag (waste material). They are so malnourished that their bones also can be seen through their skin. The lenses of their steel glasses have been mended which look like glasses after been hit by stones.
All of their time and space are foggy slum
So blot their maps with slums as big as doom.
Their time and space, everything is limited to their slum only. The slum is also full of fog that means the slum has unclear future. This foggy slum has blotted (barred) their dream world. This slum is a hurdle in life as big as doom (misfortune).
