Kittens do not sleep in the litter box because it is cold, but because they like the litter in the litter box. Kittens like granular cat litter very much and will lie on it and play. In addition, when the kitten enters a new Environment, because strangers will instinctively hide in sealed places, trying to find their own smell.
Tip:
It is common for kittens to sleep in the litter box. This behavior will change when the kitten grows older.
