Showing my age here - but I had a Little League coach in 1973 and 1974 who had his entire team doing long toss as a part of every practice. Not sure when long toss started - but I know Coach Crane was a believer back then when I was 11 and 12.
He also had us using bike inner tubes as we warmed up for our bullpens... very much like the bands of today.
On a related note, I was curious a few years back on how many kids made it from 12 years old to HS baseball. So I found an allstar program from the local little league district tourney and traced as many of the kids as I could find. Less than 50% of the ones I could find made it from LL Allstar to high school varsity player.
So how hard does a 10 YO throw? Does it really matter given the fall out rate?