There are many coding apps and websites available with more being added every day. Many of these are puzzle-based, leveled activities that teach the basic ideas of programming (decomposition, sequencing, building algorithms, loops, conditionals, debugging, etc.) but they don't let students create their own open-ended projects. This site will concentrate on apps and websites that can be used to create open-ended projects to support learning in curricular areas but that may have some puzzle-based leveled activities as well.
If you are interested in more of the puzzle-based, leveled activities for iPads, you can find links to many of them on my Coding on iPads spreadsheet - this list includes links for all ages, not just primary students.