The nanny was in a subordinate role to the husband who was an employer by definition. If he was inducing/seducing her with pain meds and flirtatious interaction:
1.) as a father he should know the nanny was a poor influence/caretaker of his children if she had a drug problem/interest in recreational drug abuse;
2.) he would be guilty of violating Federal controlled substances laws and contributing to the delinquency of a young person;
3.) his actions as a boss/superior with someone of such inexperience in the work world would be considered harrassment at least, and sexual exploitation of an employee. It is a form of coercion to be in the employ of someone who is abusing you, and confusing for a young person who is inexperienced in both sex and workplace politics. When a girl is that age, she is concerned about being accepted/liked and performing her job.
Bottom line, he is a predator of everyone around him. Yes, the babysitter's behavior was immature and misguided, but that is what makes him even more culpable, as the adult and BOSS he should have had the better judgement. It sounds like he was encouraging and playing along with the flirting because he is in love with a warped idea of himself and what sex is about.
BTW, DRIVING does not equate to MATURITY, this case is proof...