Young Adults is the vague term, but I think most fitting. Audience is this, or older.
Keep in mind, most web novels are essentially a subscription services and this implies audience with the certain level of at least semi-independent income, and many sites including *that one* are often somehow monetized. This rules out the children. A sufficiently neglectful parent may be fine with the children entertaining themselves with the smartphone, but once credit card details and thus money disappear to strange websites registered to strange counties, they are bound to notice. Not to mention children often don't react well to the written text, unless forced.
