What is the past tense of "sing"?

Hi there. Thank you for your question. Family karaoke night sounds like so much fun! In English the normal past tense form of the word “sing” is “sang.”  However, the word “sung” is the past participle, used only after a helping verb. For example; “She has sung the the song.” It's not “she sung the song” but “she sang the song.” Therefore, you could say "I sang the song", or "I have sung the song''. Both of these are grammatically correct, just remember to use 'sung' after a helping verb. (Have, has, had and so forth.) More often than not, we use 'sang'. I hope this helps and we look forward to answering any further questions you may have.