Moving my kids up to an 8 vs 8 game, I found that they still tried to play only long passes and not dribble. Break players into small groups of 4 or 5. Have them race by dribbling to end of field and back. Call out "freeze" during the race, any player that takes more than 3 steps to get control of thier ball must wait a turn before proceeding. Continue this until all players have made it to the finish line.