Edit in JSFiddle

<script>
    // Created Feb 24, 2014 by Troy Whorten
    
function toggleChild() {
     div1 = document.getElementById("div1");
     div2 = document.getElementById("div2");
    target = document.getElementById("target");
    if (target.parentNode.isEqualNode(div1))
        div2.appendChild(target);
    else
        div1.appendChild(target);
}
   
function createChild() {
     div1 = document.getElementById("div1");
     div2 = document.getElementById("div2");
    target = document.getElementById("target");
    sibling = document.createElement('div');
    sibling.innerHTML = "Sibling";
    sibling.setAttribute("class","sibling");
    if (target.parentNode.isEqualNode(div1))
        div1.appendChild(sibling);
    else
        div2.appendChild(sibling);
}
    
function killSiblings() {
    siblings = document.querySelectorAll('.sibling');
    for(var i = 0; i < siblings.length; i++) 
    {
        siblings[i].parentNode.removeChild(siblings[i]);
    }
}
</script>



<div id="div1">
    <p id="target">TARGET CHILD</p>
</div>

<div id="div2">
</div>
<br>
<button onClick='toggleChild()'>Move Child</button>
<button onClick='createChild()'>Give Target Sibling</button>
<button onClick='killSiblings()'>Kill all Siblings</button>