If you've decided to teach a beginner programming class, you are in a unique position to change a life. You can open doors that might otherwise remain closed for some students, by extending an invitation to young students who might not be exposed to computers and programming in their schools or at home.
Your class should probably be limited to about 25-30 students. Any more than that and the noise and activity level in the classroom can be distracting, especially when there are volunteers/teaching assistants working alongside the kids.
The recommended age for this class is 12 years and older, but use your discretion. Students as young as 10 could be eligible, but you might want to steer them towards graphical interface learning tools such as Scratch and Hopscotch instead.
Remember that students need to have reached a certain point in their cognitive development to be able to work with some of the abstract concepts common to modern computing. Most kids reach that point at around the age of 12.
Basic typing skills are also going to matter - even a bright younger child might not be able to type quickly enough to keep up, and that can impair the learning experience.
Both of those things need to be in place for this material to be useful and comprehensible to students.
Once you've settled on a date and venue and have planning well underway, use a free service like EventBrite to take student applications.
You'll need some basic information from your students and their parents/guardians:
You should also include a basic release form with the enrollment (a sample can be found in the repository). This ensures that parents are aware, among other things, that students may sometimes be unattended, and that you expect students to be picked up by a legal guardian at the end of the class.
Open applications about two months before your event - this gives you plenty of time to promote and get the word out.
And prepare for an exuberant response - you'll probably want to maintain a waitlist.
Your students will be the best students ever. They'll already be in a classroom mindset - the one thing they know best at this age is how to learn, because it's something they do every day. You will have to battle with some distractions, but for the most part your students will be eager and attentive.
They won't have to be there - they'll want to be there. They'll be in your class because they're excited about what you have to teach them.
That enthusiasm will be infectious.