Merlinfun is the official place to redeem your Kellogg's Grown Ups Go Free offer online.
You will need your 10 digit offer code to hand when redeeming - you can only find this inside special promotional packs of Kellogg's cereal. If you do not have this code, you will need to bring the voucher on the day of your visit to redeem the offer at the gate.
Please make sure you have read the terms and conditions of the voucher to avoid disappointment.
We hope this answers your question.