Underpaid or Just Right?

I'm having a hard time trying to figure out if I'm getting underpaid or paid just about right for my position as a nanny, or as they call me... a family assistant. Here's the scoop about me: I have a Master's degree, 10+ experience working with children (teaching, tutoring, nannying), trust-lined, and all that hoopla. I chose this field because there are no teaching jobs in San Diego right now. The Family I work for has me work 40-44hrs/week - 4 days/week (10-11hrs/day) with infant twins, and 2 older children (4 and 6) who go to school full time at $14/hr cash. I have the two older children for an hour in the morning to get them ready and take them to school and 2-3hrs in the afternoon after school. I live-out and they supply me with a "nanny car". When the twins are napping, I do household chores and/or run errands. Oh and I have been there for about 4 months and I really like the family. What do you think? I feel like I should be earning at least $2 more/hr, making that $16/hr for everything I do. My family thinks I should be paid $18/hr. Also, when should I ask for a raise? At the end of the year when the twins become more challenging? Thanks

BTW - I know you think I would know what the going rate would be, but I have never watched more than 2 children and have this many chores in a single day. My previous jobs were part time and short term (less than a year) so I never had the chance to get a raise. Also, I was working at a preschool when I finished my Masters up until the end of last year.

Hi SD ,
I think with your education and experience and chores , you should earn about 25-30/hour.That would be the real value of your work , but we all know the economy today , everyone want the best service for less money , and basically the salary is based on the mutual agreement between yoy and your employer.
You defienetly have to ask for a raise the end of your year , if you will stay that long!!!