Daycare wage pay.. Please help!?

Okay, my dad's girlfriend is running a daycare and she needs help, I am looking at working at the least 6-8 hours a day. She charged $2.00 a child $2.75 for 2 etc. We can not figure out what I should be paid to make it fair for the both of us, so she is not underpaid and either am I. Could you please help us with what I should be paid. Thanks :)