How to tell parents you are increasing your hourly rate?

I babysit for 6-8 families regularly. Half of them have been "clients" for several years. About a year ago I raised my hourly rate for all new families that reached out to me. I did not tell existing families as I did not intend to change the rate for them. Maybe that was a bad idea but I didn't know what I was doing. Now i'm at the point where I would like to move all families to the same rate.

How do I word this in a text? How do I politely say that my rate has increased, and hope they still want to use me? Do I mention that i've already been charging new families at the higher rate? Or is that an attitude? Keep it short and sweet?