I think the optimal swing, and the position that puts your body in, naturally produces a slight uppercut; especially on lower pitches. That's fine. When I see extreme tilt however, like with Dunn, or Edmonds, the angle of the bat greatly decreases the margin for error imo. And hitting is hard enough without lessening your chances.
I would drill home "down through the ball" as an important mental cue, of course making sure the kid understands it doesn't mean chop down. Chopping down and slicing the ball with backspin is completely different then staying through the ball and creating forceful backspin.
Maybe you or others on here, who have coached kids of all ages could tell me. How do you think the younger ones would respond? Would they understand the difference?
"The inference is that in the dead of the night the under-secretary of the club owner sneaks to a private telephone, summons the manufacturer, and bids him pour a little strychnine of digitalis into the old apple to make its heart action quicker. The factory gets out the ball bearings, the block rubber, and the go-juice, and the home run epidemic follows." - Paul Gallico