Yes. Each family should have their own tax number and be paying quarterly. There is no loophole for this because you still dictate everything else about the job and provide the "tools" necessary to complete the job. Also if one family takes an extra vacation, I assume the nanny will be caring for your child in your home.

Bump. I'd like to know this, too.

If I am sharing a nanny in someone else's home, do I pay the nanny as a household employee? If not (because it's not my private residence), do I need to register for an employer ID number?