Here is the full list of all 20 When The Past Was Around achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Play twinkle twinkle little star in the piano
Complete all achievements
Open all the windows
Play all the music notes
Complete Chapter 5
Break all the pots
Complete Chapter 4
Turn off the Radio Tape
Input 1915 on the safe
Complete Chapter 3
Eat all of the ice cream on Owl's side
Finish the Tea Time with Eda and Owl
Complete Chapter 2
Click bird inside the postbox
Complete Chapter 1
Tidy up Eda's room
Open the curtain
Break all of the tombstones
Complete Prologue
Look at the photo inside the drawer