referencing a child based on another

I am developing a price comparator and need to pull the bank name and category photo and the product node for each category which is a listview; (child) "child" ("categories"). child (idCat) .child ("products") receiving the id of the category in the idCat variable for each category receive the correct data? (I can already pull the category name and photo);

    valueEventListenerCategorias = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            //limpar lista
            categorias.clear();


            for (DataSnapshot dados: dataSnapshot.getChildren()){
                cat_principal = dados.getValue(Cat_Principal.class);
                categorias.add(cat_principal);

            }
            adapter.notifyDataSetChanged();

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    };'