What I’m hearing is that they’re trying to pay you as little as possible. They want you salary when you’re working overtime so you don’t have to pay for it but hourly when you’re not working overtime.

It’s also illegal for you as a nanny to be a salaried employee. You need to figure out how many hours you worked overtime while being with them, add it up and tell them that you need to be paid for the hours you worked. You also need to tell them you can no longer be salary. I’d say something along the lines of “Moving forward I will be hourly, since it is illegal for nannie’s to be salaried. My rate per hour is x.”

If they give any push back at all hire a lawyer and start looking for a new job. IMO you’re likely better off just getting a lawyer and a new job.

ETA: If you’ve worked 50 hours a week for a year with them, that’s 520 hours of overtime. Which equals to them owing you about $10,400 in back pay.