If your kitten is sleeping for most of the day, do not worry. When kittens sleep, they release growth hormones. These are essential for their development hence why young cats always seem to be dozing.
Image by Екатерина Гусева/ Pixabay
As adults, cats tend to sleep a lot too because dozing saves energy. This is an instinct evolved from being in the wild as they would need to expend their energy when hunting. If they always seem to be asleep though, you could try playing with it a little more as it might just be sleeping out of boredom.