By imagination, I mean the mental flexibility that leaps past the real world into a limitless one where animals and inanimate objects talk, ships sail on deserts and monsters are tamed by peanut butter. The youngest readers or listeners (as many aren't reading yet) don't know laws of gravity. They don't distinquish between reality and fantasy. They are learning good from evil but they also believe their parents can protect them from everything. So almost anything goes in a PB. The more outrageous the better.
The ability to access a young child's voice is gold. To re-experience the love of sounds, giggle at funny words and delight in rhyme. To play with language, rearrange it in ways that speaks to children. The youngest book lovers don't need to understand every word. They have adults to explain if they feel they must know. But the words must mesmerize. Young minds have very short attention spans. If the words don't entice them, they wander off to find something that does.
Illustrations are the other half of the PB story and they should be equally imaginative. They aren't simply pictures illustrating the author's words. They are a separate part of the story, shown in art. Picture book illustrators are masters of expression, exaggeration and whimsy. They set the tone with line and color.
I, sadly, have neither a flexible imagination nor access to a young child's voice. But I'm trying to find them and I'm having a fabulous time hanging out with writers who are as witty and playful as the books they write.