Heard it somewhere but didn't know what it was? Well, target audience is another part of your web page that you would want to spend some time on before going on to your content. Basically, target audience can be referred to as a certain group of people that you would want to focus on for your webpage. It can be of a specific age group, gender, where they live, what they do, their experience with your site's topic etc.
You should always design your web page based on what your target audience would prefer, rather than on your likes. In this way, your audience will be stay comfortable and captivated by your site.
In this case, language will have to be quite layman and able to grab attention. If difficult terms are used (such as the word adolescent), they will need to be explained to the readers. Also, you might want to have more images or animations so as to improve their understanding. You can then create a survey to find out what other websites kids from 10 to 15 often visit. Ask them why they prefer these websites and perhaps consider them for your websites. The 
Another thing you might want to find out is how people use your site. Do they browse through every single page of your website, go to the search box instinctively, or navigate through your menus in its order? Only after having a rough idea of how people generally use your site will you be able to structure your information such that it satisfies the needs of your target audience.