Are the hand-eye coordination gains from juggling real, significant, and permanent?

Hello!

My eight-year-old son plays baseball, rather seriously (travel ball). I juggle and I have introduced him to the hobby. He can't juggle yet. I have seen promising information (mainly from youtube videos) about measurable hand-eye coordination gains that can be made from juggling. My questions: Is it true that juggling significantly and measurably improves hand-eye coordination (in a way that's transferable to other sports)? If so, are these gains long-lasting for the juggler - even if the juggler stops practicing for years (but retains the ability to effortlessly perform a 3-ball cascade for example)?