Fluteman (1982)

When the small town of Minyaka suffers from a drought, a kind and mysterious stranger offers to make it rain by playing his flute; under the condition that he be paid. But after Fluteman makes it rain, and even stops it; the town council, blind by their greed and pride, refuse to pay him. Fluteman stands before the town and warns them of a curse he would bring; and so the next day the school playground fades into silence as all the children disappear into the bush... except one.

Unfortunately the movie Fluteman is not yet available on HBO Max.