With both of my daughters we learned fastball, palmball change-up (with no wrist snap), which is not the change-up either uses now, and when those were able to be spotted the next pitch was peel-drop which both still use sometimes...IMO the mechanics and releases on those are close enough that younger pitchers don't mess up anything...
In 1975 I started every student off with peel drop and then a change up. However as time went on I found out that most travel, allstar and rec ball teams do not like to call the drop I start each student off with a fast ball then change up.
Keeping in mind that I work with mostly young beginning pitchers.
Fastball for strikes
Fastball for location
When they are ready I will begin with inside and outside curves to teach them ball rotation. As the curves develop they move into the rise and drop unless their body has not developed enough for this. I have other tricks for these younger skilled pitchers whose bodies are not ready for the advanced pitches. You can give the allusion of multiple pitches while increasing her control of her body as well as her pitches.
Since each kid is different I will sometimes throw in some different movement pitches based on the natural rotation and development of the individual girl.
I like Bill Hillhouses approach.
Learning to us the fingers instead of the wrist to create spin is very important , since most colleges now are looking at a 20 RPS as the minimum for a pitcher.
I go with fastball, backhand changeup, then drop. I used to teach mostly rollover drop, but have actually gone the other way and mostly teach peel drop because I think it's easier for most to learn. I was reminded recently, however, that it's good to experiment.
I was working with a girl who was having trouble throwing the "cut under" curve, so I decided to have her try the "over the top" method instead. She still hasn't quite mastered the curve yet. But she's developed a heckuva rollover drop -- much better and sharper than her peel drop.
So as Chuck Berry would say, it goes to show you never can tell.