Tail shape behind the vent, at any age, can provide an indication of what sex the snakes are. Males will have less of a taper toward the tail from the vent. This is because this is were the hemipenis reside. Females will taper sooner. This isn't a 100% accurate way to sex, but it can give a good clue.
Here's a thread from MVF with some pictures and stuff to think about.
http://pub95.ezboard.com/fmoreliavir...picID=72.topic
For the pictured near full term dead hatchlings in the above thread link, I have not dissect them to determine sex(yet), but I'll probably try some day. Hopefully they aren't to small to mechanically determine sex.