Well that wouldn't work because Wi-Fi is the wrong choice. Buuuuuuuut if you gave them cellular data plans? Now you're onto something. The Boron by particle comes to mind as a low cost dev option. The USB should let you talk to a computer as a flash drive, you can throw an SD card on/external to it for storage, and use the modem to sync to the others. As long as they're all on battery, should be fine.