AustLit

'A boy is always picked last for sports teams. However, he is about to get a baby brother. While sleeping on the night just before his brother is born, he dreams about a world where he has a mate who helps him all the time; this mate turns out to be a grown-up version of his brother. In the dream he also finds that his mother has died and he lives with his grown up version of his little brother, who is called Simon but is nicknamed Possum. When the boy's baby brother is born his mother cleans him and admires the new born and says "What a lovely little possum". Possum also has a birth mark the shape of Australia just like the dream version of himself.'  (https://en.wikipedia.org/wiki/Undone_(short_story_collection))