Here are a few simple strategies on HOW to keep your players FOCUSED and ATTENTIVE during a training session. Remembering that your players are children – not mini adults – and if you are running a midweek coaching session, they've probably been at school all day, being forced to sit and listen to their teachers. Once they're out in the fresh air with a goal to shoot at, the last thing they want to do is listen to more lectures.

Tip 1: Keep it short
When you're explaining a game or drill to children, try not to speak for more than 15 seconds and never talk for more than 30 seconds. Give just one or two instructions, check they understand ("are we all OK with that?"), then get into the action quickly, ("right, let’s go!") and simply correct errors and or instructions as you go along, don’t keep stopping.

Tip 2: Silence is golden
Never start talking until you have your players' complete attention. Make sure balls are left to one side and keep quiet until your players are quiet too, even if it takes several minutes.

Tip 3: Avoid distractions
Face your players away from other games or activities that are going on around you and don't stand with the sun behind you as you will get better attention without the sun in the kids eyes.

Tip 4: Get down to their level
Don't tower above your players. Get down on one knee if you need to and make eye contact with every player as you speak. Don't wear sunglasses.

Tip 5: A picture is worth a thousand words
Demonstrations are a key part of football coaching, so show your players what you want them to do.
If you can't do it, find someone who can! Ask for volunteers or get an older or more experienced player to show the others the skill or technique.

Tip 6: Have rules... and apply them
It is essential to have team rules that are discussed and agreed with your players. My number 1 rule is simple: "No talking while I'm talking." But don't be too quick to apply sanctions – if you do, you'll come across as a sergeant major instead of a coach – but if a quiet word doesn't do the trick you will have to tell the player concerned to sit out until they are ready to listen. There's nothing to be gained by making a player sit out a game or drill that they didn't really want to do anyway but making talkative players sit out the first few minutes of the end-of-session fun game is a powerful deterrent.

Summary
These tips will help you avoid being embarrassed by players who refuse to listen and you should expect and encourage your players to pay attention to what you are saying. But be a little lenient especially with younger players. What you may perceive as discipline problems are really personality tendencies common to that age group: short attention spans, high energy, sociability and an inability to understand detailed explanations. Don't expect six-year-olds to act like 26-year-olds.
And remember that all children come to coaching / training sessions to have FUN and learn to PLAY football which, ultimately, is just a game. Taking it too seriously, or making practice too much like school, will result in your players switching off altogether and, in the end, they'll just stop coming.