Man people are harsh on here, although they are right. OP you need to know what you deserve and demand it. You can sit down with them and say something along the lines of:

"I've enjoyed working for you the last 6 years, however I have one concern that I need to address. I took this job with the expectation that I would receive annual raises. I've tried to be understanding of your situation and so I have not pursued it in the past. However, I need to look out for myself and if we are unable to come to an agreement about raising my salary, then I will have to reconsider my position as your Nanny."

Also you have to mean it! They may refuse, and then you have to be prepared to look for another job. This happened to me at my last job, I asked for a raise, they said no, I said OK, two weeks later I gave notice after securing a new job with better pay. I don't work in an area where there is a big demand for nannies but I was able to do it.

Good luck and please update us!

What gives. Is that you are a doormat, they figured it out, and they are using you. You claimed this Christmas was the last straw but you're still working for them. So... It's not.

They know they don't have to pay you because you are going to stay anyway. If you want more money, you need to find a new job.

Sorry, OP, but you're not too bright.

I have worked for a family for 6 years and was told at hiring that my I would receive a raise each year. I never have. Each year I ask them to review my job and ask if I will be getting a raise and each year is a different excuse, not about my job performance but about their money, travel expenses, buying a new Lexus ending up being more than they thought it was. This holiday season was the last straw for me, I typically will get a gift or holiday bonus. I know it is not required of them to gift me anything and I appreciate it but this year I hand delivered bonuses to the piano teachers, the tutors, the coaches on behalf of the family I work for. They gave me nothing. It hurt my feelings. Do you give your nanny raises or bonuses? I was promised a raise yearly when they hired me but have had no pay increase yet. What gives??