Madonna Sings Happy Birthday to Daughter Onstage During MSG Concert

Madonna gave her daughter one of the biggest birthday presents imaginable -- getting a packed crowd at Madison Square Garden to sing along and help her ring in the big 1-8.

The pop star brought out her kid, Mercy, onstage Monday night during her show at MSG and showed off her incredible talent by having her play a little piano for the arena -- that is, before Mama Bear helped lead a full-blown sing-a-long for her to celebrate her born day.

It was a pretty sweet moment ... not only did Madge come over and belt out the tune, but a lot of her backup dancers and stage crew members also rushed the stage to join in.

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