OK, thanks.Any brand of non-clumping clay litter is safe.
I have read that clumping litter is not recommended for very young kittens, because they may eat it and it expands in their stomach. It may block their intestines or something. Last time I fostered kittens, my rescue friend brought me a particular brand of clay litter that she said was safe. But I was kind of confused if that is the only brand that was safe.~ As far as I know all litter is safe - unless there is a specific warning.
I use clumping litter with no problems. Silica crystals I would not use in case kitty swallows a piece .
My kittens popped everywhere except the litter box until they were about 8 weeks old. I would try to catch them "in the act" and put them in the box. They all learn eventually . I think they self-train by watching the other cats .