function getChildren(popper) {
  return {
    tooltip: popper.querySelector(TOOLTIP_SELECTOR),
    backdrop: popper.querySelector(BACKDROP_SELECTOR),
    content: popper.querySelector(CONTENT_SELECTOR),
    arrow: popper.querySelector(ARROW_SELECTOR) || popper.querySelector(ROUND_ARROW_SELECTOR)
  };
}
Returns the child elements of a popper element