babysitting

I am babysitting for my SO coworker for a couple days next week, I have 2 little girls 5&7. the 5 yr old is not yet fully potty trained. They get dropped off at 630am-7pm depending how late they work since they are laying asphalt. I provide all the meals, snacks, ECT. my question is, how much would should I be charging? I am cpr certified. trying to get an idea