A $20 discount is provided for each additional child that is registered for the same course. However, I only know how to do this as a refund after you have registered and payed. You will be contacted when this refund has been issued.
You will be redirected to PayPal for payment and to finish your registration, after which you will receive a confirmation email.
If you do not want to create a PayPal account, just click the "Pay with a debit or credit card" link and you can pay with a credit card.
Important: Make sure you check your spam folder for the confirmation email because there is information in it about the class.