Le ballon rouge (1956)

English title: The Red Balloon.

From the Internet Movie Database:
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A boy makes friends with a seemingly sentient balloon, and it begins to follow him. It follows the boy to school, to the bus, and to church. Boy and balloon play together in the streets of Paris and try to elude a gang of boys that wants to destroy the balloon. (...) Written by alfiehitchie
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I did not like it as much as most people seem to have.