VB
<br /> Dim firstElement = xmldoc.Descendants("Child1").First<br /> firstElement.AddAfterSelf(New XElement("ChildNew") With {.Value = "New"})<br />
Or C#
<br /> var firstElement = xmldoc.Descendants("Child1").First();<br /> firstElement.AddAfterSelf(new XElement("ChildNew") with {.Value = "New"});<br />