class_docstr: An ES class, inherited from Optimizer.
  
  This is the designed class to define ES-related
  variables and methods.
  
  References:
      T. Bäck and H.–P. Schwefel. An Overview of Evolutionary Algorithms for Parameter Optimization.
      Evolutionary Computation (1993).
code: def n_children(self, n_children: int) -> None:
      if not isinstance(n_children, int):
          raise e.TypeError("`n_children` should be an integer")
      if n_children < 0:
          raise e.ValueError("`n_children` should be >= 0")
  
      self._n_children = n_children
  
imports: import copy
  from typing import Any, Dict, Optional
  import numpy
  import opytimizer.math.random
  import opytimizer.utils.exception
  from opytimizer.core import Optimizer
  from opytimizer.core.agent import Agent
  from opytimizer.core.function import Function
  from opytimizer.core.space import Space
  from opytimizer.utils import logging
label_desc: Use image node_id 5 for calling the ES obj's underlying member method code with example usage: obj.n_children(n_children) without return types