var child_element = document.querySelector("#id").children[0];
//Where # defines id and '.' a class. And 0 argument the first child element
var child_element = document.querySelector("#id").children //get all children
var doc = document.getElementById("test");
var notes = null;
for (var i = 0; i < doc.childNodes.length; i++) {
if (doc.childNodes[i].className == "4") {
notes = doc.childNodes[i];
break;
}
}
var parent = document.getElementById('test');
var children = parent.getElementsByClassName('four');