Gatsby was surprised by the fact that Daisy has a child as he saw her as a daydream rather than a woman. The main character was deeply in love with a dream girl who barely had flesh. So, she could not possibly be associated with such earthly aspects as childbearing.
The Great Gatsby book dwells upon numerous issues the modern society has to face. But the main character’s feelings for a woman remains central to the story. F. Scott Fitzgerald, the author of the book, stated that the novel highlighted social issues. The focus is on the changes that took place in the society that became highly hedonistic. It explains the way Jay Gatsby felt about Daisy Buchanan. She was an embodiment of the American Dream and a symbol of sensual love.
Clearly, symbols and dreams are far from reality. So Daisy’s daughter was something inappropriate and impossible for Gatsby. His attitude towards the girl was not hostile. For him, she was something so surreal that he didn’t believe in her existence. Gatsby learned about the child, felt surprised, and forgot about its existence the very next moment. He was fixed on the woman of his teenage dreams.
The Great Gatsby is a story about delusions and misconceptions that lead to suffering and death. Jay’s reaction to Daisy’s child was quite understandable. He wanted to indulge himself without thinking about consequences. The child could become the person who could bring the main character back to reality. But he chose to ignore the little link to the real world and followed his dream.