I coach a 10-13 year old i9 league (5v5). Here is my setup:
- 9 kids on team all 11-12 years old
- 8 are fast, 1 has a foot issue and is challenged in running and cutting
- 3 of them are crazy fast
- I have a short team, the other teams have taller kids
- We've been very successful
I use a 2-1-2 zone, 2 corners up front, a linebacker in the middle and 2 safeties. At the linebacker position I put one of the 3 crazy fast kids and based on what he and I see (I'm on field) I either have him drop back into coverage or edge right up to the line for run defense, I also play the corners up on the line to guard against the run or misdirection, although at this older age the kids don't get fooled much by it, the days of the triple reverse are gone!
I've found at this age man is tough even with short fast kids, the zone works much better, you just have to teach the kids to stay in their zone and watch the QB's eyes which they cannot do in man. Some of the taller teams play man on us and they cannot stay with our receivers. I put my challenged kid at one of the corner positions and make sure he turns the runner into the middle of the field and that is working real well, he is part of the defense and he knows it which is great.
The biggest part of our defensive success is the communication between the players, they are constantly chattering and telling each other whats going on, they are getting smart enough to see offensive formations (like shifting over when they see a trips formation) and they know who the good kids are on the other teams.
If I saw your defense and I have, I'd just throw shovel passes or short passes into the flats as Coach Rob said, when the middle of the field is open like that its dangerous - if an offensive player gets into the open many times he has one man to beat. After a few of those plays the kids will cheat up to stop the short plays and then the deep pass gets unleashed. I am much more in favor of a balanced defense, its a good mix of short and long coverage. You may bend but you probably won't break.
Good luck, FF is my favorite sport to coach, I hope my boys play on for a few more years and I hope i9 expands the league to older ages.