Is $10 -$20 a good price to babysit?

My sister in law will be taking care of my kids

My daughter 2 yr old

And my 7mo baby

It will be One day for each week

we are very close family. My husband said $20 for both kids, once a week it’s a good price? We live a few steps away. I know she won’t charge us or even ask us she’s not that type of person but we think we should still give her something even if it’s only for 2hrs. I have class it’s the reason I have to leave them and my husband works so I have no other choice but just her help.

Or what do you think it’s a good price?

$10-$20?