Hi there, Ruby!
After a 14-hour drive, it's my thinking that nothing would be more welcome than a fun-filled water park! Your seven-year-old will definitely be able to get out some of the energy built up during the ride, and no one will look twice if there is some wild cheering from all of you on the slides.
Of the two water parks on Disney property, I would recommend
Typhoon Lagoon.
Blizzard Beach is just full of action-packed slides, and does require quite a bit of climbing up the "mountain" to access the fun. Typhoon Lagoon, on the other hand, offers a wealth of activities and areas just right for the younger set that might not quite be ready for the higher altitudes.
After trying out some of the body slides and family slides, your travel party can enjoy Castaway Creek, the 2,100 foot lazy river.
And Ketchakiddee Creek is the perfect toddler/youth water spot, featuring scaled-down slides, waterfalls, water jets, and much more.
Don't miss the world's first water coaster, the Crush'n'Gusher, either!
Have a wonderful trip!
See you later, celebrator,
-Deborah B.