Do not bring the candidate into you home at once if at all possible. Go through a thorough list of interview questions, and trust your instincts. If it doesn't feel right, it won't get better. You have payroll tax obligations when you hire a nanny. Workers compensation insurance is often required.
Many families offer the nanny medical insurance.
All of these must be dealt with in the first week or so of employment. If you are uneasy for any reason, move on to another candidate. If the house is most important, hire a housekeeper. They are in high demand. Review the work agreement.