Although Laurent and Jane were twins, Jane had been kidnapped when she was six months old. Laurent had grown up lonely.
By the time he found her over twenty years later, they had already missed the period when they could grow up together.
Since Laurent had a lonely childhood, he did not want Jayden to have the same experience. Therefore, he was already discussing trying for a second baby with his wife.
The gender of the second child did not matter. He simply wanted Jayden to have a sibling