If you’ve written a book for children which needs illustrations you’d be wise to submit just your text, and leave your publisher to commission the illustrations.
Like much of publishing, this seems counterintuitive to many new writers. They feel that their work needs those illustrations in order to realise its true potential. But there are good reasons for leaving that side of the work to the publishers.
What if you go to great expense to commission a series of illustrations and you don’t manage to sell the book? Good quality illustrations don’t come cheap, and you’ll be substantially out of pocket.
Can you be sure that you’ve calculated the pagination correctly? Illustrated books have very specific page-counts and if you’ve committed to a single spread over or under the necessary amount, you’ll be in trouble.
What if the publishers you submit to don’t like the pictures? It could put them off the whole book, whereas if there are no illustrations at all, they are free to imagine it as they prefer.
What if a publisher likes the book, but the illustrator decides to hold out for a further fee before he’ll allow his pictures to be published? Or you find that you’ve not covered all rights in your contract with the illustrator, so your book can’t be licensed or sold in translation?
There are all sorts of problems involved in commissioning your own illustrations and really, it’s best not to encounter them at all. Write your text, and leave it up to your publisher to find and commission the right illustrator for it.