There are literally tens of thousands of illustrators who would be happy to illustrate a children's book series. Because you are obviously a small publisher, you want to know where to find reasonably priced illustrators as well as know what style would work well with your series. I run an art education website, an art jobs list group, and art job website.
I have companies post openings on my site as well as have thousands of people search for art jobs. All of it is free of charge. Following are a few useful links for you to browse: princetonol.com/groups/iad/jobs/careers.... princetonol.com/groups/iad/jobs/openings... princetonol.com/groups/iad/jobs/illustr.... I have a collection of links to websites that include thousands of samples of illustrators.
You can find it here: princetonol.com/groups/iad/links/artists... Searching through the artists can be time consuming, but worth the effort to get the right artist for your series.
You should also be aware that many publishers have their own stable of illustrators who they assign to projects like children's books as and when they crop up. Often, it's a case of selling the concept/story/text of your book to the publisher - if they like and want to publish it they may also want to select the illustrator they think is best suited to it.
You can seek out freelancers with an online service like Guru.com. You can set the rate and ask for samples.
There are several places where you can look for illustrators for a children's book. A few of the best places is Odesk. Odesk is a website where freelancers can place bids on work from individuals and employers.As an employer seeking an illustrator, you will describe the project and post an ad for free.
Members will send their application in to you, give a fee for how much they are willing to do the project, then ask them to send in samples of work. You can choose from thousands in a few days at reasonable rates. Second choice is craigslist.com For about $25.00 you can post an ad that will be linked to your email where potential illustrators can email you their resume as well as samples.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.