A requirement of the Mac App Store (MAS) is that all apps must be sandboxed. In basic terms this means that an app cannot access any files other than its own – a useful security measure.
This means the MAS version of OneOunce cannot access the trial versions database. As default the MAS version of OneOunce will not have your little ones feeds, picture and weigh in stats that you created during the trial. Do not worry, your data is not lost and there is a simple solution:
Open your trial copy of OneOunce. (If you no longer have your trial copy, simply download a trial copy again - it will still have access to your trial data).
Backup your trial copy of OneOunce from the built in Backup functionality.
Open your purchased MAS copy of OneOunce and restore the backup you just created.
You will now have all your stats from the trial copy. Optionally, we would also recommend you now delete the trial version of OneOunce to avoid future confusion.