from The Left-hander's Calendar, Wednesday- June 8th.
If your daughter uses her left hand consistently for many activities at the age of two years, you can be fairly certain she will be a lefty. If your son is doing the same thing, he might still switch over to the right at some point. Girls develop hand perference earlier than boys.
I also remember another one about left-handiness more prominently male versus female. Now if I could just find it.