find_child
Description:
Attempts to find the given child item with the container's stack.
Parameters:
| this | 
           a container item.  | 
      
| child | 
           the child item to find.  | 
      
Returns:
| 
           the position of the given   | 
      
Attempts to find the given child item with the container's stack.
| this | 
           a container item.  | 
      
| child | 
           the child item to find.  | 
      
| 
           the position of the given   |