Create a div for each parent? - foreach

Question

I need to wrap all the childrens of the parent with a div. In the example below I managed to put a div tag after each parent but how do I put an end /div tag at the end of the chidrens.
I tried with document.createElement, and now with insertAdjacentHTML ..., what is the best way to fix this, or the best way to encode it?
var divs = document.getElementById("container").querySelectorAll('.activ-window *');
var elements = "";
divs.forEach(function(elem){
if (elem.firstChild) {
elements += elem.insertAdjacentHTML("afterbegin", '<div id="afterParent" style="display:block;">');
elem.insertAdjacentHTML("afterend", '</div>');
}
});
document.getElementById("demo").innerHTML = elements;
<div id="container" class="activ-window">
<div id="parent1">
<div id="child" ></div>
<div id="child" ></div>
</div>
<div id="parent2">
<div id="child" ></div>
<div id="paren3" >
<div id="child" ></div>
<div id="child" ></div>
<div id="child" ></div>
</div>
</div>
</div>
It should look like:
<div id="container" class="activ-window">
<div id="parent1">
<div id="afterParent" style="display:block;">
<div id="child" ></div>
<div id="child" ></div>
</div>
</div>
<div id="parent2">
<div id="afterParent" style="display:block;">
<div id="child" ></div>
</div>
<div id="paren3" >
<div id="afterParent" style="display:block;">
<div id="child" ></div>
<div id="child" ></div>
<div id="child" ></div>
</div>
</div>
</div>
</div>
Edit for Nick:
This is with text(see Parent1):
<div id="parent1">Parent1
<div id="child" >child1</div>
<div id="child" >child1</div>
</div>
I get it with your code
<div id="parent1">
<div id="afterParent" style="display:block;">
"Parent1"
<div id="child" >Child1</div>
<div id="child" >Child1</div>
</div>
</div>
It should look:
<div id="parent1">Parent1
<div id="afterParent" style="display:block;">
<div id="child" >Child1</div>
<div id="child" >Child1</div>
</div>
</div>

Answer 1

If you want to enclose all the divs beneath each parent in a new div, you can create a new div element, move all the non-text children to it, and then add that div as a child to the original parent:
const container = document.getElementById("container");
const parentDivs = container.querySelectorAll('.activ-window div[id^="parent"]');
for (let parent of parentDivs) {
// create a new div
let after = document.createElement('div');
after.id = 'after' + parent.id;
after.style.display = 'block';
// move the parent's non-text children to it
let children = parent.childNodes;
for (let i = 0; i < children.length; i++) {
if (children[i].nodeType != Node.TEXT_NODE) {
after.append(children[i]);
}
}
// and append it to the parent
parent.appendChild(after);
}
console.log(container.innerHTML);
<div id="container" class="activ-window">
<div id="parent1">
Parent1
<div id="child1"></div>
<div id="child2"></div>
</div>
<div id="parent2">
Parent2
<div id="child3"></div>
<div id="parent3">
<div id="child4"></div>
<div id="child5"></div>
<div id="child6"></div>
</div>
</div>
</div>