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