Fair babysitting funds

Lacey • Mama to Ocean Zari 09.28.18💗 & Ollie Zander 05.22.20💙 Luna La’Rae 07.09.22💖

So one of my mom's friends wants me to watch her twin girls (five years old) for one day a week from about 7:30 to 3 for the summer, I'm new to babysitting so I'm not too sure how much is the right amount to charge? She was gonna put them in daycare but it was to expensive for her to pay $100 a week, btw I also have an 8 month old myself so what do you think would be fair to charge her? I dont wanna undersell myself but I also wanna help her out