There is the old phrase, “everything I needed to know I learnt in kindergarten.” I think this also applies to the themes that weave amongst the earliest books encountered at a young age. Aren’t the vivid animal stories captured in engaging picture books the mere precursors to the worlds of Kipling which could be the precursor to Thoreau’s Walden, which might inspire one to leap into the polemics of Michael Pollan and beyond? Might the story of friendship in Mac The Apple pave the way for The Bridge to Terabithia and Harry Potter and - the more complicated - Great Gatsby?
We run the risk of treating themes and topic areas as secondary in the earliest encounters with story. This would be a mistake.