they are young and all want to be part of the play.  it is a very long road to teach them to spread out.  teach them court corridors, (split the court into 3 from goal to goal, then have the GK in the centre third, the GD in a side line third the WD in the other sideline third, the centre in the centre third, and so on)  practise getting the ball down the court by staying on your side of the court.  once they are doing this, then allow them to move into each others third but if say the centre moves into the WD third then the WD must move into the centre third.  but be prepared that on game day that they will still tent to bunch up until it becomes more ingrained because that is what the other teams will do as well.  just be patient with them.  it is a skill that takes time.