My daughter is 7. She was jealous that I was teaching her older brother some rudimentary html and css, so I showed her how to do it, too. I set up the basic html for the page and showed her how she could type in the file and show it in the browser. After experimenting for a bit, and asking for help with styling it to have purple script font on a red background, she proceeded to type a bunch of text into the paragraph tags. When I read it, I was surprised to find that she had started a My Little Pony fanfic.
At this point, she's more interested in continuing her story than in learning what the html tags mean.