hi mark 

i think its really important to help each player understand their role or roles in the team, whether it be just for one week. highlight the importance of why they are playing that role, as at that age it may not be their only position.

i would still encourage the players to have the courage to go forward, that could be with or without the ball, 

but after each decision made by them tyr to ask them questions about why they made that choice, what implications were there(good or bad). and how they can make that decision even better next time. they will learn by the wins and fails.

but to give them freedom where ever they play is the key.

a goalkeeper can come out of their area and play a pass,

a defender can overlap

a midfielder can make that tracking back tackle on the penalty spot

an attacker can clear a corner

be specific but with freedom to play and express where ever on the pitch

Your goalkeeper will have a defined area of the field which is their primary playing position. Why not divide the remainder of the pitch into defined areas (I realize this will take some time to do) A strip down the left side of the pitch; another down the right; a defensive defined area as well as an attacking area. It will develop players by rotating their positions of play so they sample all responsibilities. As they gain  awareness of space reduce the number of defined areas. All young children want to kick the ball so their natural instinct is to chase after it. The team coach has the task of re programming the child's understanding and therefore development of play.