How Much Should You Pay a Babysitter?

I've always worried that I am underpaying my babysitters. When I was growing up, I was basically a nanny for a family who's mom was getting her masters. I was paid $1/hr for 4 kids. I thought it was just fine. Now a days, babysitters make minimum wage - or more! I've been paying my babysitters $2/per kid. So, in my case, that's $6/hr. I always worry that they get more somewhere else. I found this little babysitter payment calculator. I think it might be a little high, but maybe I'm up in the night.