If there are no children, there is just a root. You can delete the tree by setting the root to null.
Ok.... I see you cross posted this on codeguru's forums..... The more info you provide the more help you will get. Post the code you have so far, and any of the project instructions
To check if it's an empty tree, all, theoretically, you'd need to know is if the data at the root is null.
If the root is null, in theory, all should be null.