Just throwing this out there...
I think you've bit off more than you can chew. It sounds to me like you're not quite ready for this, given what you've posted here and in your previous thread. It's okay to say no. Or, collaborate with a local pro who is qualified to do this shoot and assist him/her. Because here's the problem...
If you screw this up, you're sunk. It's one thing to ease your way into the business by shooting friends/family/friends of friends. Those people understand that you're new and are a lot more forgiving. If you do this, and do a poor job, it's going to be much harder for you to find work locally with a bad reputation attached to your name.
You're talking about shooting an entire football league, which is probably a hundred kids or more. The level of coordination, planning, and execution of a shoot that size is pretty intense, and you certainly won't be able to pull it off by yourself. It's just not possible.
1) Schedule. There are 11 positions on each side of a football team, 11 offense and 11 defense. This is a little league so some kids probably play both, but there's still second stringers, coaching staff, etc...so each team is probably going to have 30 kids or more. Multiply that by however many teams are in the entire league. Each team is going to have to be assigned a block of time for their shoot. 2-3 individual shots of each kid, plus the full team shot. If you can cram all of that into a 2 hour session for each team, I'd be surprised. A shoot of this size is probably going to take more than 1 day.
2) Releases. You're going to need to make sure everyone has a signed release. It's going to take at least 1 additional staff person at the shoot to make sure this is done.
3) Order forms and payments. Who is going to collect those. If you're accepting payments, who is going to collect those?
4) Assistants. You'll need at least 1 other person just to help you pose the kids, make sure hair looks good, uniform looks good so their player number can be seen, etc.
5) Making sure each order form is assigned to each kid in-camera. With hundreds of photos being taken, you damn well better keep track of who's who. Otherwise you'll wind up with a bunch of photos and not know who the kids are, much less what they ordered, if they paid, etc.
6) Location. You'll certainly need permission to use the football field...at least that's where you should be taking these photos...and coordinate with the school/field location to make sure there's no conflict at the field and you're cleared to use it.
7) Insurance. What if someone trips and knocks over your camera, and breaks it? What if they get hurt in the process?
8) Prints and pricing. Have you figured out where you're having all these prints made and priced accordingly? Will they drop ship, or do you have to handle that yourself?
If I'm making this all sound like a huge hairy deal, that's because it is. There's a lot more to this than just showing up with a camera and hoping it all falls into place. I would never discourage anyone from hanging their jubblies out in the wind and giving it a shot, but I don't want to see anyone set themselves up for failure either.