Kittens' physical development speeds up and the weaning process begins. This a vital stage for learning from their mother and siblings.
During this stage the "immunity gap" occurs. At this time, when the level of antibodies provided by the mother are no longer enough to guarantee the kitten is protected, but too high to ensure a vaccination will be effective, the kitten is more vulnerable to disease. Sleep helps to strengthen their immune system, so ensuring kittens have a warm, comfortable and quiet place to sleep is vital.
At around two weeks a kitten's milk teeth develop and the weaning process begins. After a while the kittens will begin to show an interest in their mother's solid food and they can begin to transition from a milk-only diet. Their immature digestive system means that it's important they get easily digestible food that meets the specific nutritional needs of this stage.
As this stage progresses, kittens start to interact more with their litter-mates, and they begin mutual grooming. They will start to actively play, exhibiting running, pouncing and stalking behaviors, and their sight is fully mature.
By the fourth week, smell is fully mature and hearing is well-developed. By the sixth and seventh weeks they begin to develop adult sleeping patterns, motor abilities and social interaction. Key social skills develop through interaction with litter-mates, and learning is achieved through observation of their mother's behavior.
As kittens become more mobile and adventurous, it is important to "kitten-proof" the environment. This is also a key learning stage, so making sure kittens have access to toys and other stimulation is key. Regular handling and interaction with different humans will aid their confidence as adults.