<input id="txtBox" type="text"/>
<span> <input id="txtBox" type="text"/> <span>エラーです</span> </span>
var txtBox = document.getElementById('txtBox');
var span = document.createElement('span');
var parent = txtBox.parentNode;
parent.replaceChild( span, txtBox);
span.appendChild( txtBox );
var errTips = document.createElement('span');
span.appendChild(errTips);
errTips.innerHTML = 'エラーです';