It doesn’t look like this promo is available anymore. You can see the most up to date promoations from Nickelodeon Universe here:
Register your child’s birthday (Age 15 and under) at Nickelodeon Universe and your child will receive a FREE unlimited ride wrist band on their birthday!
Shortly after registration, you will receive a confirmation email voucher for FREE admission. On your child’s birthday, bring the printed email voucher and valid ID to the Nickelodeon Universe Guest Service desk to redeem your FREE all day unlimited ride wristband. You will be required to show a valid picture ID or a document verifying your child’s date of birth (like a birth certificate).