Youth baseball is full of dads volunteering to coach the kids. As it should be. The more we help them, the more we help the kids.
I would keep it real simple with 9yo's. A stable posture and balance is the foundation of a good delivery and that's where I'd start. Get the kids to keep there heads upright and moving only towards the target. Try to eliminate any movement side-to-side, back towards 2B, or up-and-down although recognize that their heads will move down a little as the back leg bends and due to striding down the mound.
Strategies for eliminating unnecessary head movement include putting them into a more athletic position - one in which they have the strength to stabilize their posture - by having them put more (or less) bend in the knees and waist. Also, watch for knee lifts that are too high for their strength to accomodate without excess head movement.
Once they're doing good with posture and balance, start to pay attention to their glove arm - get them to control their glove instead of dropping it, pulling it or flying open with it.
For more on these concepts, see The Art and Science of Pitching in book or video (just the Mechanics video of the video series) here: