Let's start with a doozy of a sentence: The short-legged, fluffy, orange Pomeranian walked down the dirty sidewalk, past the shady green trees, and into her large square yard with the tulips, daisies, and daffodils next to the two story blue house with the wrap-around porch.
While this does give you quite a visual, it's pretty exhausting to read and a bit long for the attention of a three-year-old. Visual description is often a place where a picture book author can make deep cuts, or not include it all. Here are three reasons why you can toss those adjectives out the door.
Written Description Is Redundant
One great thing about picture books is they have pictures! The pictures do the work of showing the visuals so the words don't have to. Why tell the reader and listener the pig is wearing a red rain jacket with yellow buttons when they can look at the page and see it? Or that the park has a swing and a slide and a bench and a...you get the idea. The park will be there on the page.
Let's go back to the sentence with the Pomeranian. Reread it and think of everything written there that would be shown in pictures. The short-legged, fluffy, orange Pomeranian walked down the dirty sidewalk, past the shady green trees, and into her large square yard with the tulips, daisies, and daffodils next to the two story blue house with the wrap-around porch. Most of the words in this sentence can be cut out.
Illustrators Don't Like It
When an illustrator gets a manuscript, they develop their own vision for the story. They don't want to be told what every tiny detail looks like. That would leave no room for them to experience and interpret the story with their own creativity. Think about it. Before you wrote a story, would you want someone telling you every single detail to write?
You may want to cling to the idea that the pig must be in a red raincoat with yellow buttons. After all, that's how you pictured it as you wrote. But is that really the most important part of the story? Will the story not be the same if the pig is in a blue raincoat, or gasp!, no raincoat at all? Giving the illustrator that creative freedom results in a better product because they use their expert artistic and visual skills to come up with things that are often even better than what you imagined.
This doesn't mean you shouldn't include a visual detail that is essential to the story. But you should leave room for creative interpretation by the illustrator as much as possible.
It Inflates Word Count
Getting the word count down is often one of the biggest challenges of revising picture book manuscripts. Traditional publishers want manuscripts to be around 500 words or less. There is more wiggle room for indies, but it should be below 1,000. (See this post on word count for more info.)
You have to chop, chop, chop as much as you can. Visual description can take up a lot of those precious words and like I said earlier, it's redundant with the pictures. Trim it wherever you can and don't let it inflate your word count. (See this post for other ways to cut word count.)