Kittens don't actually sleep during the day and not at night. That is a misconception! Kittens actually sleep a lot, both during the day and at night. They need around 15-20 hours of sleep a day.
Sleep is crucial for kittens' rapid growth and development. They need lots of rest to build their muscles, bones, and nervous system. Playing and exploring can be tiring for small kittens, and sleep helps them conserve energy for their next burst of activity. Sleep is also essential for the development of their brains and cognitive abilities.
It might seem like kittens sleep during the day because their sleep cycles are shorter than adult cats, meaning they might wake up more frequently for feeding and playing. They are also more active at night due to their natural instincts; in the wild, kittens would be more active at night when their mother is hunting.
So, kittens don't sleep only during the day. They sleep a lot, both day and night, and their sleeping patterns might seem different from adult cats.