kind of depends how old they are, and how much experience you have! but if you have more than a few years' experience and they are active kids, i would charge at least $10 an hour.
$10 an hour- and an extra $10 if u have to make dinner (usually should be made ahead of time for u to warm up)
Hi, I babysat for many years in my time, and you can charge hourly if you like, but usually when I babysat that long I would do a daily rate, especially if you have to drive them somewhere. I usually charge $120 a day for a time period like that but I had been babysitting for 13 years. I was CPR certified in infants/ children and adults. I had a car. I had numerous recommendations.
Also take into consideration what you will be doing in the day and the age. If they are younger and have to be played with you charge more. If they are more independent... you charge a little less. If you plan to take them swimming or some activity where they have to be supervised you charge a little more. Figure this all in before so you have an idea of what you are asking and why... if the parents happen to ask.
Good luck and have a blast!