Nanny here and I disagree with this.
It really depends on how long you have been in a job and how high you are on the payscale. If you've been in a job for a long time and received many raises, you may not be able to find a new job starting out at what you were making.
+1
+2. It also depends on the responsibilities. If you cared for two kids for several years and earned raises to a $24/hr rate, it is silly to think that you could easily make the same rate for a single child with less responsibilities. You could try, but you could be unemployed for a long time. It's the job that determines the rate.