A major goal of yours should be sparking interest and a desire to learn more from each class the students attend. A good way to do this is to have each class give the students something they can walk away with and use immediately in a manner they appreciate.
For example: class one could cover the basis of what a web page is, and how the html, css and so on make the page. Don't go into detail, just hit the high lights of each, compartmentalizing the web page elements and their respective purpose. Don't say how they are constructed, only describe what they are used for - html=content, css=layout, php=logic and so on. Then give them one example of editing a MySpace page, showing something simple for students seeing this for the first time, and something advanced for the students that already use MySpace Editors for their own pages.
Class one, you give them a mental picture of a web page and then show them how to modify a MySpace page. That should get many students' attention. In the following classes, touch upon each area a bit, exploring your student's interest and letting the class explore. They may go into Flash games or widget development, it's hard to say. But in each case, it's not to hard to take baby steps into a complex area. Remember, you're not making CS graduates here, you're giving a class of students a "guided interactive tour" with the goal of sparking their interest and creativity to learn more.