<div id="multicol">
  <div id="firstchild" style="widows:2">
    line 1, first column<br>
    line 2, first column<br>
    line 3, first column<br>
    line 4, second column<br>
    line 5, second column<br>
  </div>
  <div id="secondchild" style="break-before:avoid;">
    line 6, second column<br>
  </div>
</div>

#multicol {
  columns: 2;
  column-fill: auto;
  column-rule: dashed thin;
  line-height: 20px;
  height: 100px;
  background: yellow;
}