I'm a little confused about the age range of your group, but I highly recommend having in-house or attending a hackathon or two. Its not a "hack into the mainframe" type event, but a "hack together some sort of project" event. I'm not sure what there is for high school/middle school but its a pretty big community in college with Major League Hacks (
http://mlh.io/) and a lot of college hack-a-thons encourage high schoolers to attend.
The cool thing about a hackathon is it forces you to complete a project in a short amount of time and you learn a fair amount doing them, and then if you win, at least in the college ones, there are a lot of cool prizes (items and/or cash) you can win and its good exposure to companies.
As far as activities, in the class I TA for we have labs that focus on using a specific concept: if statements, loops, state machines, arrays, pointers, etc. We use arduinos and try to make it fun (key word: try). Anything with easy access to accelerometer data that you can then drop from a large height makes for a really fun lab where the students have to use accelerometer data to tell if the item is being held, in free fall, or bouncing/landing: and then compute how long it fell (you may have to guide them through the physics/algebra of that).