This list is from my Steam library, however I haven't yet played all of them:

   - Deponia  
   - The Detail
   - State of Mind
   - Black Mirror II
   - The Dark Eye: Chains of Satinav
   - Disturbed
   - Earthshine
   - Edge of Reality
   - Edna & Harvey: Harvey's New Eyes
   - Fighting Fantasy Classics
   - The Forest of Doom
   - Jericho's Prophecies
   - Memoria
   - Mirt. Tales of the Cold Land
   - Scarlet Hollow - Episode 1
   - Agatha Christie - The ABC Murders
   - Life is Strange
   - Life is Strange: Before the Storm
   - The Lion's Song
   - Misadventures of Laura Silver
   - Omen Exitio: Plague
   - Syberia
   - Syberia II
   - Wonderlust

If the parent want a few more suggestions:

  - Primordia
  - Strangeland
  - Machinarium

Excellent, thank you! I've already played Machinarium and absolutely loved it but I've wishlisted the other two. Great suggestions!

In addition to the sibling comment, I suggest these as personally assessed to be of high quality:

     - The Last Door
     - Gemini Rue
     - Resonance
     - Whispers of a Machine

Thanks for the suggestions, these all look good!