code: func (p *basePlan) ReplaceChild(child, newChild Plan) error {
  	for i, ch := range p.children {
  		if ch.GetID() == child.GetID() {
  			p.children[i] = newChild
  			return nil
  		}
  	}
  	return SystemInternalErrorType.Gen("ReplaceChildren Failed!")
  }
docs: // ReplaceChild means replace a child with another one.