I would offer $1-2/HR based on rates in your area as well as what you can reasonably afford. 😃

What an odd amount at 21 per hour. How did you come up with that particular amount?
Raises are usually based upon ability and appreciation.

$25 sounds good.

$40 seems steep. Based on what I've read on these threads I've seen $26-30/he for multiple kids

I'd at least get her to market rate of $25hr which is a steal to retain someone you love part time. I'd pay up to $40/hr for a reliable great part time nanny or sitter.

I have a college-aged babysitter or "nanny" that helps with my 5 year old daughter 3 days a week. I pay her $21/hr, and we just love her- now that a year is approaching I'd like to give her a raise; how much of a raise is appropriate? I'll add that I don't give health insurance or any of the standard work benefits, was never part of the plan and she still lives with her parents.