He fucked the baby girl with the help of his sister. Both enjoyed abusing babies while babysitting. This time though, the mother was helping. She held the 4yo so that he could fuck her daughter rough and hard while the sister began frigging the mother, telling her dirty stories of what they had done to other babies. As the baby cried they sat the mother on her little face and had her bring herself off on the childs face. Everyone was sexually turned on.