children of pointer pointing to Node are always NULL C++

I`m creating a game with AI using recursive calling , i have a struct called "Node" , when filling them with new int[5][5] they are filled but when i return and call other function like when i call a fun called "bestMove" to loop within children THEY are all pointing to NULL , for an example

struct Node 
    {
    int state[5][5]; 
    if(root)//parent = null;
       else
    parent = root;child[i] = null;//after looping
    }

void fill_new_state(Node* childPointer)
    {
    if(everything is Ok) //and its Okay
    childPointer = new Node();//with linking to parent and all...
    childPointer->state[row][col] = bla bla bla//fill 
    return;}

void expandChildern(Node* root)
{
  fill_new_state(root->child[i])//looping
}

void bestMove(Node* root)
    {
    Node* best = root->child[0] //if not null and it is not null
    //loop and chose the best 
    root = best
    }

void main()
{
struct root = new Node();
expandChildren(root);
bestMove(root);
}

in the function fill_new_state(Node* childPointer) the child is filled and its not NULL but after returning fromfill_new_state(Node* childPointer)exactly in the functionexpandChildren(Node* root)` the child is NULLed