Change of Fate: The Cold Prince and the Modern Maiden

The night ended tragically for Melissa when she met with an accident which took her life.
However, the next moment, she was alive and turned out, she had transmigrated into a novel and engaged to a Duke! It was said that this fiancé of hers was cold-hearted and only cared about work and not interested in women! But why did he follow her around? He even kissed her every chance he got.
Whatever, since she couldn't avoid her fate, she would play her character well. But, who's this adorable young child?
"What're you doing here? Go back to your chambers!"
"I'm your husband. I'm sleeping here with you."
"Mother, I'm sleeping with you and Father."
"Son, get out."