I'm no rules interpretor or anything, but grabbing a jersey (from behind) sounds like an intentional to me. Girls/boys 5yr olds/11yr olds... what's the difference?

IMO I think it's best to teach them "the right way" to do things at a young age, so they don't do it wrong when they get to the next level. ie moving in/out the free throw lane spaces once the shooter has the ball. I had a mom/coach swear that I was unfairly awarding team A an extra free throw for that violation.