Here is the full list of all 26 Children of Silentown achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Collect the "Mysterious paintings" sticker.
Choose the Children's Song.
Collect the "Windmill" sticker.
Collect the "Doll" sticker.
Get the cat as best friend.
Collect the "Glass shards" sticker.
Collect the "Huge Snail" sticker.
Collect the "Flower of hope" sticker.
Collect the "Big metal ruler" sticker.
Collect the "Blue's drawing" sticker.
Collect the "Coal's fur" sticker.
Collect the "Complicated padlock" sticker.
Collect the "Depths of the well" sticker.
Collect the "Mysterious footprints" sticker.
Collect the "Puppy" sticker.
Collect the "Broken toy" sticker.
Collect the "Spyglass" sticker.
Collect the "Trumpet" sticker.
Collect the "Hairball" sticker.
Collect the "Egghead Lucy" sticker.
Collect the "Lucky charm" sticker.
Collect the "Old kettle" sticker.
Get one of the children as best friend.
Choose the Mom's Song.
Choose the Song of the Forest.
Choose the Song of the World.