Nothing completely world-wide, it seems.
I'm just a hobby musician, but before joining this stack I had never heard of the type of "grades" people seem to use to measure proficiency with musical instruments. I live in Sweden, and it doesn't seem to be a thing here. There are entry exams you need to pass to get into music schools and academies, of course, and there is collaboration between universities to standardise some tests, but nothing as organised as what I see people discuss here, and certainly not for children.
Just to be sure, I asked my girlfriend. Her parents are both professional musicians, and she's been playing the violin in various organised contexts since she was a kid. She majored in music in high school, continued at Folkhögskola(no idea how to translate..) and then spent 5 years at university to become a music teacher. A teacher should know about this, if anyone. She had never heard of anything remotely like the "grades" either.
There might be something that's fairly global, I don't know, but at least in one country it's not a thing.