<div class="container">
  <div class="inner">Hello</div>
  <div class="inner">Goodbye</div>
</div>

{
  $('.inner').wrapInner('<div class="new"></div>')
}

{
  document.querySelectorAll('.inner').forEach(element => {
    const wrapper = new DOMParser().parseFromString('<div class="new"></div>', 'text/html').body.firstChild
    
    wrapper.append(...element.children)
    element.prepend(wrapper)
  })
}