I also took inspiration from three main sources. The Grimm Fairy Tales, Nursery Rhymes, and myths and tales from Scandinavia and Eastern Europe.
The nursery rhymes and Grimm Fairy Tales are excellent starting points, as the characters are all recognisable straight away. The fun begins when you start to subvert the plots and/or exaggerate the characters. It is all too easy to imagine a twisted, emaciated Big Bad Wolf, stalking the player through a claustrophobic forest, or a well forever abandoned due to a haunting by Jack and Jill.
In contrast, the other folk tales are less well known, however they contain far more macabre events and creatures than the stories we know and love, and all of them would make fine additions to a fairy tale game. Highlights include the Czech story of Otesánek - a tree root shaped like a human child, which never stops growing with an insatiable hunger, consuming everything it can - or the Scandinavian jötnar. Trolls and giants of incredible strength.
I will be delving into all these things in more detail in the future, exploring how each one can bring further inspiration and enrich my ideas.