When I first posted a top free apps list, it was the Top 10 Free Apps for Kids (all ages). I used the site clicks, and still do, to determine the order as I wanted to the list to be a reflection of which free apps.
Lock iPAD screen & iPhone screen so kids stay within the app
How to lock iPAD or iPhone Screen, so Children Stay within the App You Want Them to? - No More Accidental App Deletion or Unwanted App Re-arrangement! -- very helpful iPhone iPad tips for parents and teachers.
TECH Free Educational Math Apps: Number Rack, Geoboard, Number Pieces Basic, Geometry Pad + More! I can use this in my classroom to help differentiate learning for my students. It can be used in a center or for intervention with certain students.