insertBefore()

js/script.js

function funMake() {
var val = document.getElementById('d1');
var elP = document.createElement('P');
elP.innerHTML = 'Hello World!';
val.insertBefore(elP, val.childNodes[1]);
elP = document.createElement('P');
elP.innerHTML = 'To be or not to be?';
val.insertBefore(elP, null);
}

function funMake() {
var val = document.getElementById('d1');
var elP = document.createElement('P');
elP.innerHTML = 'Hello World!';
val.insertBefore(elP, val.childNodes[1]);
elP = document.createElement('P');
elP.innerHTML = 'To be or not to be?';
val.insertBefore(elP, null);
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<div id="d1">
<p>Привет Мир!</p>
</div>
<script>
funMake();
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<div id="d1">
<p>Привет Мир!</p>
</div>
<script>
funMake();
</script>
</body>
</html>