I am asking this question on behalf of some of my extended family. I do know the child myself, but apart from one or two occasions where I have watched them it is mostly from a distance. For all intents, he is my little cousing we shall call Eric, age 8. If I use the word 'we', it is for the benefit of readability.
Eric is a child who would commonly be referred to as gifted. He is a very thoughtful child, and has an easy time figuring things out on his own - especially when it comes to subjects he is very interested in (which is almost everything, depending on his mood). He has also figured out that his parents don't have all the answers and will usually rely on books from the library to confirm or challenge his 'discoveries'.
In particular, he has a great interest in physics and he has self-derived some basic laws in statics and classical mechanics. The process is usually him sitting with a pencil and piece of paper in a state in which he doesn't want to be disturbed, looking at things around him or simple things he has constructed out of Household objects. When eventually done and he has checked he is in fact correct, he is always enthusiastic about sharing his work. Although he tends to isolate himself for this period, his parents feel they should nurture his talent and process so they do no interfere.
Unfortunately, his other major hobby also includes a manner of seclusion as he likes to write fiction. This he is a lot less eager about sharing, and he is visibly offended when someone reads his work accidentally or tries to peek over his shoulder. At one point it got bad enough that he even started becoming reluctant to share his scientific 'discoveries'.
This reached its pinnacle a little over a month ago when his parents found some of his writing in his room. Although the themes were beyond his age, it was not graphic or offensive in any way. Eric, however, obviously saw this as an invasion of his privacy and has since taken to writing ALL his work in a self-taught form of shorthand (We confirmed it is actual, he can repeat passages of his own work verbatim if so asked about the science stuff even days later).
We fear this manner of seclusion could harm him in the long run, but do not want to interfere with the development of his talents. The usual advice of Parents.SE in all cases seems to be to be or get involved as much as possible in all activities of the child but this is something the child obviously does not want. When attempts are made, he prefers to go do something else with the person (so he is not entirely anti-social!)
How do we encourage him developing his talents while still being able to shield him from harmful thoughts he may express in his prose, and generally supervise and - really - parent?