Babysitting 2 toddlers and 5 yr old

☁️ • 👩‍❤️‍💋‍👨 💍 ❤ Happy mommy 🥰 Love my babies 💙💙💜

Wondering how much I should charge to babysit 3 kids (2 separate families). 1st family is for a 1.5 yr old. 2nd has a 1.5 old and 5 yr old. I myself have a 4 yr old, 2 yr old, and 1 yr old. So it can get busy. I babysat them once as a favor and they gave me $90 total for all 3 kids. I watched them for almost 4 hours. I live in Indiana btw. Now they've mentioned they can probably have me babysit more often and mentioned same pay regardless of someday having less kids (not sure about hours) also in the summer they might include a 7 yr old once she's out of school. I'm not sure if $90 was fair for 2 toddlers and 5 yr old for almost 4 hours.? Help? I'm currently unemployed right now and have thought about babysitting on the side but I don't want to be taken advantage of just because we're family. I forgot to mention they are my husband's nieces' kids were taking care of.