If not a law as that would remove the enjoyment of coaching and striving to competition; then a professional ethics review board that oversees 'junior' sports of all kinds. Local and state authorities need to work with Sports Professionals to determine the length of time a young person can pitch. Currently, for a twelve year old, I do believe 70 pitches per game is the designated limit. The problem is no one is enforcing that so much as 'recommending' that. Young athletes across this country are being pushed way beyond such limits at all levels.
Coaches are playing 'junior' sports as if their careers depended on it. The kids are getting hurt. Those children are being abused. Not so much by parents whom may not understand the techniques in playing sports, but, by coaches both volunteer and paid.
Junior sports needs guidelines that everyone adheres to, otherwise, their future as an athlete will be ruined before it truly begins and one trophy on a shelf collecting dust over the years won't substitute for a lifetime of enjoyment and social interaction that leads to a successful life across every spectrum and emotion.
There should be a law. But. Better than that 'Ethical Reviews' of standards acceptable to junior athletes. Their time will come. When it does .... everyone stand back !
