Hi, my 8 yr old son gave me £5 of his xmas money to buy this app for my Samsung Galaxy Ace II, which we downloaded on Xmas day. He's played it once. Since then we can't even open the app. We just get a message that "The application Minecraft-Pocket Edition (process com.mojang.minecraftpe) has stopped unexpectedly. Please try again." We then get the option to force close or report.
Try deleting the app (you can still download it again, don't worry). On recent Android versions, hold the app icon and drag it over the Uninstall button that appears. Then, go back to Google Play and download the app again.