Practices for youth players should be focused on individual mastery of the ball and creativity! For younger players, skills development is infinitely more important than winning the game. The KYSA Coach Education Series provides an excellent opportunity to learn more about age appropriate training for player development. There are also many resources on the web. US Youth Soccer has published a manual to assist coaches in player development called The Best Practices for Coaching Soccer in the United States. Here's a link to the manual.
A couple of key things to consider when organizing a practice: