Simple Tree Syntax Error

I'm creating a real simple tree. No sorting and every node can have
infinite children.

// TreeNode.h

#ifndef TREENODE_H
#define TREENODE_H

#include <iostream>
#include <iomanip>
using namespace std;

// forward declare the tree class
template< class NODE_TYPE > class Tree;

// template definition of tree node
template< class NODE_TYPE >
class TreeNode
{
    // be friends with the tree class
    friend class Tree< NODE_TYPE >;

private:
    typedef TreeNode<NODE_TYPE> Node;
    // can have infinite children
    std::vector<int> children;

    NODE_TYPE data;

public:
    // constructor
    TreeNode( const NODE_TYPE &d ) : data(d)
    {
        // allocate memory for children nodes
        //children = new std::vector<TreeNode< NODE_TYPE > *>;
    }

    // accessor
    NODE_TYPE getData() const
    {
        return data;
    }
};

#endif

That is the declaration for my tree node. G++ keeps saying
std::vector<int> children; has a syntax error. Sure enough if I
comment the line out, everything compiles. I'm going nuts though
trying to figoure out the error, I dont see it.

Help!