6 Answers

If  the box is dirty, they will stop using it. You must clean it out frequently.

 The kitten may have an UTI.

If you have other cats, the kitten needs his own litterbox and needs it to be very clean and in a quiet place.

I agree with Ann.   They enjoy cleanliness and privacy just like their parents.

A clean litter box is a must have, and it should be place in a private place. Cats will not use a dirty litter box. 

The kitten can be ill, the cat box is dirty, or you live in clutter and the kitty is confused. I'd take the kitten to the vet.

Cats communicate through scent via urine,they also mark their territory with urine.I dont know at what age they start to do thisbut it is something you will have to get used to.