I don't mind taxes and since they worked, in part, on tobacco, I have reason to believe they'd work on sugar or fatty foods.
That said, fixing this problem goes far beyond taxes. I think the main solution is by increasing health education in schools. By education, I do not only mean reading textbooks in a classroom, I mean required physical education, gardening lessons and healthy eating lessons with cooking where possible. Moreover, just like kids have to science projects, kids can do healthy eating projects of many variations. Furthermore, if a student gets a "note" to get out of gym or other health related classes, then those exceptions should be handled the same way as situations with kids who can't take math in regular classes. They must do their own individualized programs. I've always thought that school should be about both mind and body, so it's time to make "body" a priority as well.