move_child
  
  Description:
  public abstract void move_child (
int old_position, 
int new_position)
  
 
  
    Moves a child to a new stack position.
    Parameters:
    
      
        | this | an item model. | 
      
        | old_position | the current position of the child. | 
      
        | new_position | the new position of the child. |