How much should I charge for babysitting, per hour?

Well, first of all, I live in Upstate South Carolina, bc i know that makes a pretty big difference in the price, and I'm 13, and i've never babysat before. I have taken a Red Cross Babysitter's course, with CPR and things like that. I'm going to babysit a 4-year-old and a 10-year-old for like 6 hours a day, everyday (weekday), for like the whole month of June. I of course can't drive, but the parents do want me to take the kids to the pool, which is walking distance, once in a while. How much should I charge per hour? And how should I tell them how much they owe me? Like if they never ask me how much to pay me, I don't want to just straight out say "I charge $(w/e it may be) per hour), i think that's kinda rude. Any advice? THANK YOU SOOOOO MUCH! I really need to know.