Scratch is such an awesome tool, it really is hard to find a good next step after it. Python is a common one, but presents some awkwardness if you want to do graphical games. It's also highly desirable that kids can get their friends to play their completed games on their smartdevices, and Python can't do that in any meangful way.
Javascript is a good next step because it's ubiquitous, and has a syntax that leads in all sorts of other directions. The problem is finding a tutorial pitched at the right level.
http://s2js.com is a Javascript tutorial aimed at kids who are very comfortable with Scratch. Instead of teaching all of HTML and javascript, it aims to teach as much as you need to produce the sort of games you were doing in Scratch, but more scalable and able to the run on your smartphone.
S2JS is tutorial, development environment and deployment platform in one. It explains Javascript in terms of Scratch, showing equivalent examples in each. Free.