This is actually not a complete answer. Unless your income from each family is less than $2,100 per year, it is their legal obligation to register and hire you as a W-2 employee, otherwise they are subject to tax fraud and evasion. Research "nanny tax." Few people know about and adhere to these laws, but they are indeed laws that have been put in place to protect both the nanny and the family. I am a nanny. I don't know how your agency works, but it would be wise for you to research nanny tax laws to make sure they are compliant with them.
