I have a babysitter who comes to the house and stays with my three-year-old son while I work. She’s asked if she can start bringing her two-year-old niece along with her. I don’t mind having another child with my son, but I kind of feel like I’d be paying the sitter to take care of her own niece. On the other hand, I’m afraid if I refuse, she’ll quit to take care of her niece exclusively. What do you think would be best?