I think that in many ways, yes, Tristram knows a lot more about the world than most children his age. But in other ways, like his father, he is unknowing in the ways of interpersonal interactions (friendships, but also familial relationships). Things that come easily to someone like Emily are a mystery to him. He understands his father very well, and to him the way that he is and the way that they live is completely normal. But, he will not have escaped noticing that other families do not live the way they do; he has been ostracized for his 'differentness' for most of his life, which is what makes his friendship with Emily and her accepting of him - and John's accepting of Sherlock so very special.