I wasn't especially impressed when I first saw this book. A is for apple, B is for balloon, C is for cow, basic stuff. The only thing interesting was "X marks the spot" instead of "X is for X-ray or Xylophone".
Then I realized that I'd seen many of the creatures in Z is for zoo earlier in the book.
So I re-read it. Several re-reads later, I realized that there was a tentative story in this book. Do the women and the man love each other? They write letters. Hearts are a periodic motif. The woman paints, the man explores. Do they miss each other?
So maybe a toddler won't understand that. But this is an alphabet book they'll read past toddlerhood.