Returns a list with with categories under the given parent.

        :param str|None parent_alias: Parent category alias or None for categories under root
        :param bool only_with_aliases: Flag to return only children with aliases
        :return: a list of category objects

def get_children_for(self, parent_alias=None, only_with_aliases=False):
        """Returns a list with with categories under the given parent.

        :param str|None parent_alias: Parent category alias or None for categories under root
        :param bool only_with_aliases: Flag to return only children with aliases
        :return: a list of category objects
        """
        self._cache_init()
        child_ids = self.get_child_ids(parent_alias)
        if only_with_aliases:
            children = []
            for cid in child_ids:
                category = self.get_category_by_id(cid)
                if category.alias:
                    children.append(category)
            return children
        return [self.get_category_by_id(cid) for cid in child_ids]