Not sure about your area specifically, but as far as I know with my networking with providers all over the country (I am a 15 year provider), there is NO standard on this issue. It is up to every individual provider to set rates and any discounting or altering rates as they see fit.
Some might have alternate rates for age changes (infant, toddler, etc), some may do the potty training deal. Many, like myself, do NOT change the rate at all. Actually mine only ever go up with inflation.
For me, a child goes from needing alot of supplies like wipes and baby food and cereals (and possibly formula if they opt for the one I provide), to using a ton of toilet paper and me needing to use alot of extra Clorox wipes and other cleaners to clean up their potty messes and misses, along with more laundry for hand washing (or buying more paper towels for the increase in handwashing). Also bigger kids eat more foods and use more art and craft supplies, etc. There is always something.
So, for me, the amount of expenditure on various supplies stays fairly constant no matter the age of the child, plus each age has its own challenges that still require as much attention. For me, its a bottom line thing. I am not willing to drop my price a few bucks a week when a child gets older, when they still cost me the same (or often more) to care for. Plus with the price of everything else going up and up...for me, its a no go.
Just wanted to offer another perspective you might not have been thinking of....