four to five weeks
At this stage, move the kitten into a larger box so you can introduce a small litter box. Never use clumping litter as many kittens will try to eat the litter as part of the exploration process. Use a plain clay litter or a litter made from paper or wheat products. Use a small-sized litter pan with low edges so the kitten can get in and out easily. One of the best first-time litter pans are the plastic paint roller trays you can buy at any hardware store. With small sides, and sturdy feet, they take up less space and kittens do well with them. The kitten will usually need to use the litter box just after waking up and after meals.
To teach your kitten to use the litter box, put him in, take one of his front paws and make scratching movements with it in the litter. At first, he will probably just play in the litter box and may have some accidents. He will soon catch on, though. The best teacher for litter pan manners is another cat. A kitten learns best by example, because sometimes, in this area, humans can fail at teaching this. Don't become frustrated if he doesn't cover his waste. Some kittens never do, that is why mom-cats are so important - they teach these manners quickly and easily.
Also at this age, he will really enjoy playtime and will begin to play with his toys more. He can walk and run in short bursts. It is now time to begin weaning as he is ready to eat semi-solid food.