Игорь

<ul class="menu">
    <li class="first">1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li class="last">5</li>
</ul>

const menu = document.querySelector('.menu')
        console.log(menu.firstElementChild)
        console.log(menu.children[2])
        console.log(menu.lastElementChild)
        console.log(menu.children[menu.children.length-1])