Show don't tell involves more than images...it is about immediacy. Whenever you're reveallng action right in the moment, you are showing and that's definitely a big part of picture books. The IMAGES are the gift of the illustrator but there is far more to a picture book and far more to showing than visuals.
Picture books and beginning readers are a mix of
showing and telling just like all the other forms of writing...they just leave out the visuals because someone else carries that burden.
Any time you are portraying a specific moment of story time, you are showing. When you talk in generalizations, you are telling.
Insert comment from Carrie: "Oh! It is really that simple?"
As with ANY story, picture books are a mix...For instance (from WHERE THE WILD THINGS ARE), "The night Max wore his wolf suit [showing, specific story moment, it wasn't just any night...it was the specific night when he wore his wolf suit...] and made mischief of one kind and another [telling, we back away and generalize the badness by compressing time with a generalization], his mother called him "Wild Thing!" [showing, specific moment where his mother spoke] and Max said "I'll eat you up!" [showing, specific moment when Max spoke] so he was sent to bed without eating anything [telling as it compresses time by not giving us the quote where the mom actually spoke and sent him to bed without supper]
Isn't that a great way to think about it?