Weekly rate?

Hello everyone, I'm needing some advice on how much I should charge for babysitting. I'm currently a sahm but there is a couple with two children who I know very well who are looking for a part-time nanny to watch their kids after school. They would like for me to do it since I know them and their children very well. They said that I can bring my daughter since it will only be from 2-5:30 during the week, so my question is what would be a good and fair weekly rate? I don't to ask for too much, but not too little. What would you pay? I have a rate in mind but I want opinions, especially from parents. I also have a certificate in Early Childhood Education and pursing my Associates, and I have 7 years of experience. It's only two children ages 5 and 7. I will be picking them up from school. Thanks.