What's the best lens for shooting a graduation *** concert with 500D?

I'm a newbie in DSLR and will be shooting my kid at his graduation *** concert in an auditorium. I have a 18-55mm IS (kit lens), 50mm F1.8 (prime lens) & a 55-250mm IS (zoom lens). I don't own an external flash yet. Which one of my 3 lens can be optimized & the camera settings & if a flash is necessary? Alternatively which other lens is recommended as I don't think I would be using a tripod during the event. Thank you!