As the saying goes, some things are taught, and others are learned.
I don't have an iPad, so I couldn't try this app, but these are just my thoughts on kids' applications in general, not the app itself:
I agree that in a learning-based program, a mission of some kind would be helpful, but too often, creators of these apps think it's good enough to put in a smiling dinosaur, or a silly animal friend and that'll do the trick. It does not.
I have a 7 year old, and he is just starting to like to "create" on the computer. He loves Sploder.com for creating games right now, but programming doesn't interest him much. If I told him to move a dinosaur across the screen he'd look around for his 4 year old brother who still likes smiling dinosaurs. At 7, which I think is a good early age to start programming, they are already into monster trucks, clone wars, and big time action. No more cutesy stuff. If that dinosaur didn't devour Jedi's, I don't think he'd like it much.