And what would our wives do with all the free time?  More personal training sessions at the gym?  More Shopping?  An expensive hobby? So your real expense for hiring the nanny is now closer to 100k.

My honest answer is that we would never hire such a full-time position regardless of income.  Maybe that's because the youngest is 6 and doesn't require full-time care.  And we can hire out cleaning and eat out at the club for a fraction of 65k/yr.