Yes you can, please make sure to check the terms & conditions of any promotion and follow the instructions from where you received the vouchers on how to redeem these.
Merlinfun.com is the official place to redeem your Kellogg's Grown Ups Go Free or Mates Go Free offer online. This website takes you through the booking process step-by-step.
To book click here.
If you have a query or require more information, please visit the Kellogg's Grown Ups Go Free FAQs.