Been working a lot with the 10-12 y/o pitchers the last few years and here the signs that seem to have worked good for us.
1 finger= 4 seam
2 fingers (pointer and pinkie) = 2 seam
fist = change up
pointer and middle finger wiggle like scissors= cutter (or type of cut fastball I show a few kids)
like a previous poster said tap the left or right shin guard for inside or outside.
point up and catcher stands late to waist one high… be sure your pitcher knows to throw high (out of good connection high) to get that free swinging fastball hitter
And if you have that exceptional young pitcher with the awesome control… we will give a thumbs up (shake wrist) with a two strike count like 1 and 2 or 0 and 2… the catcher shows the batter he is setting up inside then last second he jumps to outside for the pitcher to throw a low and away change or the little cutter. A year ago when my boy would be catching and a certain little 11 y/o was on the mound they struck out so many kids that year doing this it was sick.
Lastly catcher lightly rubs dirt with glove … pitcher better be wasting one low.
Obviously the last few things mentioned will only be for a select few pitchers at this age.
hope this helps as it has worked very good for me the last several years