Great question! Your child absolutely can play on more than one device. Please be advised that logging into multiple devices can increase the chance of losing data when switching from one device to another. In order to avoid the loss of data, it is important to:
(1) Play online regularly (i.e. using wifi)
(2) Double check you are synced before logging out and switching devices
(3) Have one designated player per designated tablet
Can two children both use the app on WiFi?
If both tablets have followed the rules above prior to leaving WiFi, then yes, you may have two children play offline, on two different devices, using two different players. However it is important to sync both players and log out after you get back into WiFi.
If you have any other questions or need more support, please email firstname.lastname@example.org.