Unlike a babysitter, a nanny watches (one or more) children on a regular, routine basis rather than being called when they are needed, like a babysitter. My source compared nannies to being "like a second mother," as they really get to know the child they're working with. That being said, nannies tend to have more responsibilities than babysitters, which are both physical (like feeding, bathing, changing diapers, etc.) and emotional (validating feelings, teaching lessons, etc.).