Big question! Help!

I have a 2.5 y/old & I will also be nannying 2 other kids (aged 5 months & 3 y/o). I will be watching them along with my own child for 5 days a week for 8-9 hours per day. How much should I charge. I’ve tried looking up babysitting rates around my area. Let’s just say I’m in Northern California... I have plenty of experience working with children. I’ve taught elementary for 6 years. I’ve babysat many times in the past. So altogether I have about 10 years of experience total. I don’t want to overcharge, but as a current SAHM I also need the income.

Thanks in advance!