I have worked for my family and I never used to receive payment for that. I used to work for free. However, I used to receive pocket money from my parents. This was the time when I used to work for free. However, I never mind it at all. Things became hard when I was forced to seek a job.
I would never feel comfortable asking my family to pay me money for playing a part in the family business because everything about the family's business is also part of me. I'm sure my own children are still going to benefit from the family's business. This is why I don't see it as something that is necessary for me to demand any sort of payment for helping out my own family's business.