Here are some shots from dance photos from a salsa dance party in Austin:-
http://www.flickr.com/photos/adatta/...7601677782666/
The light was low, the hit ratio was low as well. All shots using ISO1600 & 30 f1.4 lens.
If the dance involves moving fast for the kids, an f1.4 lens would be critical to get any kind of motion freeze. Take lots of shots, shoot RAW and do not hesitate to go ISO 1600.
If the light is semi decent at your event, or the kids do not move too fast, then a f2-f2.8 lens just might cut it. ( I use the 35f2 as often as I can as it shoots much better than the 30 wide open, but that 1 stop of 30 is becoming rather critical player)