It's a Small World is a boat ride in Fantasyland at Disneyland. While it's not a "must do," it is also recommended.
Walt Disney created It's a Small World as a tribute to the United Nations' International Children's Emergency Fund [UNICEF] for the 1964 New York Fair. Artist Mary Blair designed the unique scenes of children playing around the world, while Robert and Richard Sherman wrote the ride's unforgettable theme song. It's a Small World became a huge hit, so, after the fair, Disney moved the ride to Disneyland, where it continues to operate to this day.
Walt Disney World