I have read somewhere that a knuckle doesn't start to knuckle until about mid 50s (because the air doesn't really attack it on lower speeds) so you need at least to be able to hit 70 on your fb to throw an effective knuckle (because you cannot reach your FBs speed on a knuckle you need to be able to throw harder). that might be an explanation why most "kid knuckles" (any kid experiments with it) don't really work.
a lot of kids try to guide in a 35 mph knuckle or so (pushing it like a shot putter) which of course doesn't generate any movement and gets hammered. you need to throw it relatively hard to make it move and not push it.
I think walks are overrated unless you can run. If you get a walk and put the pitcher in a stretch, that helps, but the guy who walks and can’t run, most of the time he’s clogging up the bases for somebody who can run. – Dusty Baker.