Is SomeText ok in XML node, if there are Childnodes? Is the below code valid?
<main att="123">SomeText
<child>sample</child>
</main>
Whether your example is a valid XML document depends on the Document Type Definition you wish to validate it against. It is well-formed, tough. That is, nothing in the XML specification forbids you to write such documents.
Is it possible to have text and child elements, see: http://www.w3schools.com/schema/schema_complex_mixed.asp
It depends on the xsd that you are validating against.