Doubt of RecyclerView in Firebase (Android / JAVA)

I have this node called " Orders " in my Firebase database, this node stores as children nodes, the unique ID of each " Order em> ", the ID, in turn, has the same ID, the rout of the user who requested the order, the status, and a node" orderItems ", which stores the products requested in the order.

My idea is to capture the data of each order and recycle them with RecyclerView in a Cardview . However, I manage to capture the individual data (without children), but I do not know how to capture the child node " orderItems ", do you work with ArrayList or how could it be done?

I attach the ViewHolder code

public class RecievedOrderViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

public TextView txtRutUser,txtProdName,txtProdQuantity;

public RecievedOrderViewHolder (View itemView){
    super(itemView);
    txtRutUser = (TextView)itemView.findViewById(R.id.txtRutCliente);
    txtProdName = (TextView)itemView.findViewById(R.id.txtProductName);
    txtProdQuantity = (TextView)itemView.findViewById(R.id.txtProductQuantity);
}




@Override
public void onClick(View v) {

 }
}

And the Activity code where the RecyclerView is loaded

public class RecievedOrdersActivity extends AppCompatActivity {


RecyclerView recyclerViewOrders;
RecyclerView.LayoutManager layoutManagerOrders;
RecyclerView.LayoutManager layoutManagerOrdersProducts;

FirebaseDatabase db;
DatabaseReference tableOrders;



FirebaseRecyclerAdapter<Order, RecievedOrderViewHolder> adapterOrders;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_recieved_orders);

    db = FirebaseDatabase.getInstance();
    tableOrders = db.getReference("Orders");


    recyclerViewOrders = (RecyclerView)findViewById(R.id.listOrders);
    recyclerViewOrders.setHasFixedSize(true);
    layoutManagerOrders = new LinearLayoutManager(this);
    recyclerViewOrders.setLayoutManager(layoutManagerOrders);


    layoutManagerOrdersProducts = new LinearLayoutManager(this);

    loadListOrder();






}

private void loadListOrder() {


    adapterOrders = new FirebaseRecyclerAdapter<Order, RecievedOrderViewHolder>(Order.class,R.layout.order_item,RecievedOrderViewHolder.class,tableOrders) {
        @Override
        protected void populateViewHolder(RecievedOrderViewHolder viewHolder, Order model, int position) {

            viewHolder.txtRutUser.setText(model.getRutUser());




        }
    };

    recyclerViewOrders.setAdapter(adapterOrders);



 }
}

So far, I only set the user's routine, but I do not know how to access the values of the orderItems node, and capture that data and then set them. Because I understand that in the adapter as a parameter, the POJO class is placed and then used to call " model.getAtributo () ". The drama is that " orderItems ", contains objects of the POJO Product class, this is my doubt.