Return children grouped regarding the grid description

def childgroup(self, field):
        """
        Return children grouped regarding the grid description
        """
        cols = getattr(self, "cols", self.default_cols)
        width = self.num_cols / cols
        for child in field.children:
            child.width = width
        res = list(grouper(field.children, cols, fillvalue=None))
        return res