def do_find_children_near_mouse(self, x, y):
cell = self._grid.find_cell_under_mouse(x, y)<EOL>if cell is None: return<EOL>child = self._children[self.do_get_index(*cell)]<EOL>if child is None: return<EOL>yield child<EOL>
Speed up the search for the child widget under the mouse based

This reimplementation is faster than the default implementation, which 
simply checks every child widget for collisions with the given mouse 
coordinate, because it searches underlying the grid layout instead.  
This takes advantage of the following two facts:

1. We know that only one widget can be under the mouse, so we can stop 
   the search as soon as we find that widget.

2. We only need to check for collisions in the direction of the layout 
   (i.e. horizontal for `HBox`, vertical for `VBox`), because we know 
   that all the child widgets will overlap in the opposite direction.