Most kids like to be yelled at, anytime they miss or do something stupid, go crazy and start yelling at them. Pointing and screaming, also during the first game try to get ejected to make a point that you are for real!
As far as training goes have them do sprints for 30 mins or more, it will make them run faster and it's not alot for you to do
“Never argue with a idiot, because first they will bring you down to their level. Then beat you with experience.”