My kids are pretty easy, so I pay teenage babysitters $5/hour and my younger, less experienced baby-sitter $3.33/hour (I usually have her for a few hours at a time so I pre-pay $20 for 6 hours). The older baby-sitters usually feed the boys dinner and put them to bed. The younger one mostly comes to entertain the boys while I am home, trying to catch up on my chores. When she gains more experience, I'll leave her alone with them more and then pay her more.
I don't think he should list his rate on his business card. He may want to keep the price somewhat flexible to allow wiggle room for the number of children, level of difficulty, frequent customers, and in case he decides to raise his rates across the board after realizing the work involved.