How to hide child field collection using jquery
Can you replace the code in your JS file with the following:

(function ($, Drupal, drupalSettings) {

  'use strict';

  Drupal.behaviors.myModuleName = {
    attach: function (context, settings) {
        $('#node-student-form .field--type-field-collection .field--name-field-child-english-info').css("display","none"); // Child FC 1 
        $('#node-student-form .field--type-field-collection .field--name-field-child-maths-info').css("display","none"); // Child FC 2
    }
  };

})(jQuery, Drupal, drupalSettings);


This is based on this article
The attach() function ensures that your code runs each time an Ajax call is made