JSFiddle - React, Tailwind, and code Playground

HTML

<div class="counter" id="counter">
    <button class="adult-minus" id="adult-minus">минус</button>
    <input type="text" name="people-count" class="adult-counter" id="adult-counter" value="0">
    <button class="adult-plus" id="adult-plus">плюс</button>
</div>
    <!-- <div class="col s-4 list-1"><label for="text8">Фамилия взрослого №1: <span>*</span></label><input type="text" id="text8"></div><div class="col s-4"><label for="text9">Имя взрослого №1: <span>*</span></label><input type="text" id="text9"></div><div class="col s-4"><label for="text10">Отчество взрослого №1</label><input type="text" id="text10"></div> -->

JavaScript

var adultMinus = document.querySelector(".adult-minus");
  var adultPlus = document.querySelector(".adult-plus");
  var adultContent = document.querySelector(".adult-counter");
  var list = document.document.querySelector(".list-1");
  var listTemplate = list.cloneNode(true);

  if (adultMinus) {
      adultMinus.addEventListener("click", function(event) { 
          event.preventDefault(); 
          if (adultContent.value > 0) { 
              adultContent.value--; 
          }
      });
  }

  if (adultPlus) {
      adultPlus.addEventListener("click", function(event) {
          event.preventDefault();
          adultContent.value++; 
          document.body.appendChild(listTemplate);
      });
  }