My daughter is 16yo and gets a variety of amounts. She usually leaves it to the family to pay what they think is fair. She babysits next door neighbors and gets $10/hr for their two kids (3 and 6yo). Sometimes they need her early in the mornings and they pay a premium (and she's usually available). She sits for another family and gets $10/hr--they have 3 kids 4, 6, and 8. She sat for another neighbor the other night from 6pm-midnight and got $25, which is a bit low for our area (sitters usually get at least $5/hr here), but it was an easy sit for one child.
I pay her $5/hr to watch her 4yo brother (and keep an eye on her 10 and 13yo brothers, not that they can't watch themselves), when I pay her (if we're going out, not if I'm at the store, a meeting, etc). I expect her to clean the kitchen, etc, but she'd have to help do that even if I were home.
T&B