DOM MoveChildNode

HTML

<div id="fieldset">
fieldSet
</div>
<div id="submit"></div>
<div>
    submitButton
        </div>

CSS

#fieldset {
    border:2px solid blue;
}
#submit {
    border:2px solid red;
}

JavaScript

var fieldset = document.querySelector('#fieldset'),
    submit = document.querySelector('#submit');
while (submit.hasChildNodes()) 
    fieldset.appendChild(submit.firstChild);