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.
Choose the Song of the World.
Get one of the children as best friend.
Collect the "Flower of hope" sticker.
Collect the "Hairball" sticker.
Collect the "Spyglass" sticker.
Collect the "Mysterious footprints" sticker.
Collect the "Puppy" sticker.
Collect the "Broken toy" sticker.
Collect the "Coal's fur" sticker.
Collect the "Complicated padlock" sticker.
Collect the "Big metal ruler" sticker.
Collect the "Blue's drawing" sticker.
Collect the "Depths of the well" sticker.
Collect the "Huge Snail" sticker.
Collect the "Old kettle" sticker.
Collect the "Glass shards" sticker.
Collect the "Doll" sticker.
Collect the "Windmill" sticker.
Collect the "Mysterious paintings" sticker.
Get the cat as best friend.
Choose the Children's Song.
Choose the Mom's Song.
Choose the Song of the Forest.
Collect the "Lucky charm" sticker.
Collect the "Trumpet" sticker.
Collect the "Egghead Lucy" sticker.