Linked list loops endlessly

Linked list loops endlessly

I'm writing a simple linked list implementation for the sake of learning.
My linked list consists of node structures that contain an int value and a
pointer to the next node. When I run my code, it loops endlessly even
though it should terminate when it reaches a NULL pointer. What am I doing
wrong?
#include <stdio.h>
struct node {
int value;
struct node *next_node;
};
struct node * add_node(struct node *parent, int value)
{
struct node child;
child.value = value;
child.next_node = NULL;
parent->next_node = &child;
return parent->next_node;
}
void print_all(struct node *root)
{
struct node *current = root;
while (current != NULL) {
printf("%d\n", current->value);
sleep(1);
current = current->next_node;
}
}
int main()
{
struct node root;
root.value = 3;
struct node *one;
one = add_node(&root, 5);
print_all(&root);
}