Different price for children in Woocommerce

I thought about using product variations but I want the user to be able to add both quantities into cart at once, without having to add first adults and after children.

I'm quite new to programming so I definitely don't know the best practices to achieve what I want, but here's what I tried so far was:

Created an additional field to receive the children discount in the product admin page. So the price for adults will be for example $100, and children get $10 discount.

/* create field in product advanced */
function create_child_discount_field() {
    $args = array(
    'id' => 'child_discount',
    'label' => __( 'Discount for children', 'cfwc' ),
    'class' => 'custom-field',
    );
    woocommerce_wp_text_input( $args );
}
add_action( 'woocommerce_product_options_advanced', 'create_child_discount_field' );

/* save field */
function save_child_discount_field( $post_id ) {
    $product = wc_get_product( $post_id );
    $title = isset( $_POST['child_discount'] ) ? $_POST['child_discount'] : '';
    $product->update_meta_data( 'child_discount', sanitize_text_field( $title ) );
    $product->save();
}
add_action( 'woocommerce_process_product_meta', 'save_child_discount_field' );

Created input fields in the product page like so:

add_action( 'woocommerce_before_add_to_cart_button', 'custom_qty_fields', 5 );

function custom_qty_fields(){
        echo '<div class="custom-field">
                <p>Quantity of adults:</p>
                <input type="text" name="qty_adults" value="" title="Qty Adults">
             </div>
             <div class="custom-field">
                <p>Quantity of children:</p>
                <input type="text" name="qty_children" value="" title="Qty Children">
             </div>';
}

Now as I don't know how to send these quantity fields and calculate the value, here's what I did:

I have hidden the original Woocommerce quantity field using css (opacity: 0) and used jquery to calculate the qty of children + qty of adults, and then set the result in the hidden woocommerce quantity field. So let's say for example the user inputs 5 adults and 2 children, jquery will calculate 5 + 2 and set 7 to the woocommerce standard quantity field, so the cart will have a total quantity of 7.

Then what I want to do is, calculate the quantity of children times the children discount field set in the product, and set the value as a discount using the cart calculate fees action:

add_action('woocommerce_cart_calculate_fees' , 'add_discount_for_children');

function add_discount_for_children( WC_Cart $cart ){

    $discount = ??? //no clue on how to do that :(

    $cart->add_fee( 'Discount for children', -$discount);
}

I really don't know the best practices to achieve this and I'm probably doing it in a very bad way, but I hope you guys can understand better what I want and point me in the right way.

Thanks again!