Players can juggle, do some short passing, play keep-away, and get a few shots on goal prior to the game. Warm up the goalkeepers with help from the parents. Pass goalkeepers a variety of balls, progressing from easy passes to shots. Once the keepers are warmed up, they can go in goal and the team can take full-force shots.
Here is a link to a warm-up routine. It is appropriate for about age 9 (Under 10 teams) and older: docs/Simple%20Warm-Up%20Routine.doc
Here is a video of “dynamic stretching”, as well: http://www.youtube.com/watch?v=XCysoP3a9wg