We have a Kindle Fire (mine), a Nintendo DS, and an iPhone (mine) that the boys can use. The iPhone is the most popular because of Minecraft. Prior to their knowledge of that game the Kindle was definitely the most popular. The Kindle also requires less management on my part because I don’t have it on a phone plan so they can’t use data outside a wireless connection, and generally the permissions are set once across all apps. With the phone I have to set up permissions separately for each app. I think we’ll need a 4th device soon as our 4th child is starting to use the Kindle some.  Ideally this will be a 4th thing vs a duplicate.  But, they’re pretty much only all in use at the same time when we travel long distances (see post from Sept 17, 2014) so this is not something I have to think about any time soon.