Hi Zoe and welcome to the Disney Parks Moms Panel.
It's lovely to be able to answer a question from a fellow Brit!
I completely understand your concern and as a starting point, I am going to recommend that you read a post called "A Guide to Walt Disney World Attraction Vehicles and Seating: Magic Kingdom" which was written by fellow Moms Panelist
Erin F, for the unofficial website www.touringplans.com.
This post contains detailed information and a photo guide about all vehicle and attraction seating at the Magic Kingdom park (similar posts are available to view for Epcot, Disney's Hollywood Studios and Disney's Animal Kingdom) and will allow you to see exactly which rides and attractions you will be able to enjoy as a family in one go.
If we can be of any further assistance with the planning of your trip to the Walt Disney World Resort, please feel free to visit us again at the Disney Parks Moms Panel website and ask another question.
Wishing you a magical holiday filled with memories which will last a lifetime!
Emma