Hi Gemma & welcome to the Disney Parks Moms Panel.
First of all, let me tell you that my family absolutely love the Disney Dining Plan!
At the Walt Disney World Resort, there are a few dining locations which require full prepayment at the time of booking. These dining locations include
Cinderella's Royal Table, the Hoop-Dee-Doo Musical Revue, Disney's Spirit of Aloha Dinner Show and Mickey's Backyard BBQ.
When you make an Advance Dining Reservation at any of these dining locations, you do need to prepay in full at the time of booking.
Do not worry though as when you arrive at Cinderella's Royal Table on the day of your dining reservation, simply tell your server that you wish to use your Disney Dining Plan meal entitlements for the meal and they will deduct the required Table-Service meal credits for each person in your travel party and at the same time will refund the prepaid amount back to the credit card which payment was taken from at the time of booking.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma