What is a reasonable rate of a pay for a part-time Nanny?

I'd be watching 3 girls (ages 7, 3, & 1) from 7a-4p three days a week. They live 5 minutes away from me & no driving would be required once I got there. They just want the kids to have interactive fun-mostly outside going to the park, coloring, playing in their backyard, etc. No housework-just serve a light lunch & snacks. I am 27 years old studying for Bachelors in Social Work with focus on Child Welfare. I love being a Nanny and think this gives me good experience working with families. Any feedback helpful. Thank you!