def do_find_children_near_mouse(self, x, y):
cell = self._grid.find_cell_under_mouse(x, y)<EOL>child = self._children.get(cell)<EOL>if cell is None: return<EOL>if child is None: return<EOL>yield child<EOL>
Find the cell under the mouse, then yield its widget (if it has one).

The default implementation of this function iterates through every 
child widget searching for the one(s) that are under the mouse.  This 
search is O(n).  Here we can do it in O(√n) by iterating through just 
the rows and columns, since that's enough to uniquely identify the cell 
under the mouse.

The widget in the identified cell may not be under the mouse, but that 
will be checked by `Widget.__find_children_under_mouse()`.  See also 
the documentation for the base class method.