Three sourpuss Parks Department agents put the squeeze on a 10-year-old girl in Riverside Park yesterday, slapping the tyke with a $50 ticket for hawking lemonade without a permit.

Clementine Lee, who lives just blocks from the Upper West Side park, had dreamed of opening a lemonade stand since last year and took advantage of yesterday's beautiful weather to set up shop.

"It was such a hot day I figured people would want a cold drink," the aspiring juvenile juice mogul told The Post.

Business was booming for Clementine and her photographer dad, Richard, 49, for the first 20 minutes at the stand on West 73rd Street and Riverside Drive.

The father-daughter team was able to sell 10 glasses of the ice-cold drink for 50 cents each and the dozen chocolate chip cookies they baked.

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