Johnny ran down the road.
Johnny ran like a crazy weasel down the road.
Johnny sprinted like an insane hippopotamus down the road.
Do these opening lines all say the same thing? Yes.
Do they say it in the same way? No.
Which sentence would best suit a picture book?
The first sentence is dull. The words show no imagination at all. But it’s for a picture book, so does that matter? Won’t the pictures make it more interesting?
The second sentence conjures a more specific image in the reader’s head. An image that could be reinforced by the pictures. So far, so good. But what if Johnny IS a weasel? The words and pictures would be doing the same job. You don’t need to show he’s a weasel and say he’s a weasel at the same time.
The third sentence uses more exciting language. Perhaps too exciting? Would the audience understand the word ‘insane’ or would that be better shown via the pictures?
There is an element of alchemy to illustrated fiction which is difficult to judge. Much of it comes with practice, with ‘feeling’ your way. Certain things are worth remembering, though. Never write dull text and assume the pictures will carry you along. Don’t be overly complex either. Instead, when you are writing, focus on those elements which the pictures might not be so good at conveying. How is Johnny feeling? Excited? Scared? Excited AND scared? Complex emotions are often better conveyed in words than pictures. How fast is he moving? Short snappy sentences can often build speed and momentum more effectively than static pictures. Back stories, characterisation, relationships: these are all areas where the words can offer more than the pictures.
And of course, don’t forget that hook. Why IS Johnny running?