I don't see the code for the constructor.
Assuming there is no cyclic formed by any SuffixNode and you default
pFirstChild and pNextSibling to NULL if they don't point to anything, you
can just write:
SuffixNode::~SuffixNode()
{
delete pFirstChild;
delete pNextSibling;
}
You can also easily verify by using valgrind in any case.