A few apps I tried last fall with the group:
Pettson's Inventions (no photos of this visit, sorry!)
The first two apps are invention-building apps and are good to do in the order listed. Pettson's Inventions solutions have one right answer whereas Inventioneers can be solved in multiple ways. Both are by the same app developer (Filimundus) and so they have a similar feel, but I like them both for different reasons. The kids seemed to really engage with these apps and did a nice job of working together to problem-solve each challenge. No one finished all of the free portions before the end of my visit, but a few came close.
For our winter series, I'm going to be trying out a series of comic-creation apps. Stay tuned for more app-ventures!