Ale Abreu’s “Boy and the World” unleashes the exuberance of a child on the harsh realities of Brazil today. It’s both the best children’s animated film since “Inside Out” — you might call it “Outside In” — and, unexpectedly, a more stirring depiction of the deadening modern megalopolis than most heal-the-world documentaries.

The curious, nameless boy — his face is like a shirt button — is at first our portal to the unfiltered beauty of the fields and jungles of rural Brazil. Abreu’s bouquets of crayon color and jazzy sound design explode on the screen, treated as an arena to roam left and right, up and down. Then the tyke’s journey plunges into the depths of reality when he hops a train, joining the spindly migrants heading to the city in search of work.

What follows is a jaw-dropping sketch of towering cities and mechanized factories that brings in dark wit and satire (and clever collage) without abandoning the child’s wonder. Abreu and his film’s music makers further set up a rousing duel of leitmotifs: the cacophony of the brown-gray city, apparently in the throes of a fascist takeover, versus a recurring parade of folk music accompanied by a florid phoenix.

Not the most subtle critique, but this is a children’s film, after all, and it acquires a primal purity by avoiding intelligible dialogue. (The few spoken lines seem to be played in reverse.) It’s like some lost, globally conscious colorfest from the 1970s, reinvented with Abreu’s verve.