I remember you asking about what litter to use once the kittens are old enough to teach them how to use the litter box. First off, you have to make sure the litter box is low enough. They should sell litter boxes specifically for kittens at any pet store. Also, the best litter to use for these widdle ones is clay litter. Do not use any kind of scoopable litter or Crystal at all, as kittens have a tendency to eat some of the litter and it is not good for their system.
It can cause some serious health problems for them.

Also, here are some pictures to show you how to tell a female from a male.