I think you might be underselling your sessions a bit -- understanding how to effectively independently learn is a non-trivial skill that not everybody has mastered, and just being available to facilitate things and answer questions can be very valuable to your students. Having regular sessions that impose some structure and providing a small community of peers who share similar interests can also be helpful.
In any case, one idea is that you could perhaps try and help guide your students towards working on their own, independent projects. I've found that students (especially ones who are self-teaching) often have difficulty applying what they've learned to build programs on their own -- it seems making the jump from working on guided exercises to fully independent projects is non-trivial for many people.
What you could do is try and make sure your students all make it over that "jump" in some fashion. One idea for doing this might be to slowly start weening students off Khan Academy and have them work on a mini-project.
In particular, here are some of the things I've found seem to make that "jump" hard for beginners (and so are things you can help with):
Idea formation: beginners often find it difficult to imagine what's even possible with code (if statements and loops feel very far removed from websites, mobile apps, games, etc to a novice), and to understand how to connect their existing interests to code. (If a student is interested in games, sure, that's an obvious connection, but seeing how to write code to do things related to music, English, politics, knitting, sports, etc can be non-obvious.)
What you can do here is provide example project ideas, help students brainstorm, and perhaps do some preliminary research yourself so you can point students in interesting directions.
Project planning and problem decomposition: your students will likely need help scoping out a project and creating a realistic timeline appropriate to their level of progress and the amount of time they have. You can help them identify how to break up their idea into smaller, more manageable sub-goals, suggest some initial tasks, help them outline their overall program structure, etc...
Setup: most projects will need students to install libraries and setup their dev environment in more sophisticated ways then most tutorials cover. They will definitely need your help here -- setup can be incredibly frustrating, even for experienced devs!
Independent learning: Learning how to work through tutorials, read documentation, and compose effective google queries are all skills that more or less need to be trained. This usually happens implicitly through experience, but just being available to answer questions, give impromptu mini-lectures on related topics, etc can make things go much more smoothly for the students.
Debugging: Same sort of thing; debugging is hard, you can teach them strategies, help prevent them from being frustrated...
That said, you'll have to plan this carefully to avoid overloading your students. It's very likely that many of them practice coding only during your sessions and weren't planning on coding in their spare time (since it's the summer, after all!). Ideally, you should try and motivate them to work outside your sessions, but you should prepare contingency plans if that doesn't end up happening. Trying to complete even a small project in only 4 to 5 sessions will likely be a bit of a stretch, depending on how long your sessions are.
You can perhaps partially solve this by talking to your current students about these concerns to try and get buy-in if you're planning on having your next sessions be a continuation, or to directly state your expectations when advertising your sessions or something.
