I have a potentially great babysitter, who is 19, qualified and the daughter of trusted friends. She is about to start baby sitting our dd (5 months) next Saturday. She lives with her boyfriend, whom we have never met. She has asked whether or not she can bring him to sit with her when she babysits. As we don't know him, I am not sure that I want him in our house, but on the other hand we trust her and want her to come back. (We are considering her as a nanny). What do you think? Am I over-reacting?