re: 3 movies to capture the thrill of cinema?

I feel like small children don’t have the attention span for a 3 hour movie, let alone a 4 hour movie. I wouldn’t show a young kid (under 10) anything over 2 hours long. That rules out some of the great epics like Lawrence, LOTR, Gladiator, The Patriot, Braveheart, Master & Commander, Blade Runner, The Last Samurai, Interstellar, The Prestige, and Kingdom of Heaven.

OP definitely had a great selection of movies. Some others that I feel would also work well include:
Men in Black
Raiders of the Lost Arc
ET
Star Wars: A New Hope
Terminator 2
The Matrix
Scott Pilgrim vs The World
Goldeneye
Iron Man
The Highlander
The Rock
Back to the Future