Hi and firstly, welcome to TCS.
It is completely normal for the kitten to be still nursing from his mom at 6 weeks. He will most likely begin to be interested in her food and will start eating it so if you haven't already, you can put a small bowl or saucer of canned kitten food down for him. As the mom-cat is still nursing, it's OK if she eats it too. Also put a small bowl or jar-lid full of fresh water next to the food. He will learn from his mom about eating food and lapping the water, though he will most likely still nurse from her for another couple of weeks. When the mom-cat has had enough, she wil stop him nursing as part of his weaning process.