JSFiddle - React, Tailwind, and code Playground

HTML

<div id='parent'>
    <div class='slide'>A</div>
    <div class='slide'>B</div>
    <div class='slide'>C</div>
    <div class='slide'>D</div>
    <div class='slide'>E</div>
    <div class='otherdiv'>F</div>
    <div class='otherdiv'>G</div>
</div>

JavaScript

$(document).ready(function(){
    console.log($("#parent").children().eq(2).nextAll().find('.slide').length);
});