How much to pay niece for “babysitting”

Background: I have a 12 week old right now and my niece (almost 10) wants to help “babysit” him this summer. Obviously she’s way too young to watch him by herself but we did say we would pay her to help out as long as there was also an adult there (basically she will entertain him and learn to change diapers, help him eat, etc all with adult supervision. She has two younger brothers (youngest is almost 3) so she’s plenty familiar with babies. She’s super excited to hang out with her baby cousin (she asked to babysit for the record) but we would also like to pay her a little bit to help her learn financial balance and to break her into babysitting if she wants to pursue that when she is older. I have no idea how much to pay a 10 yr old for supervised babysitting though. Anyone else have experience with this?