I have so many art books, between me and my fiancée we have books stacking up, we've run out of shelf space. I have a few suggestions though I don't think I have anything that is specifically geared toward children's illustration. But it's all knowledge that is applied how you desire so. 
If you're looking for books to learn from, I don't think you can do any better than learning from the man, the myth, the absolute legend that is James Gurney. These are fantastic books you could pull from for the rest of your career.
• Color and Light - James Gurney
• Imaginative Realisms - James Gurney
For visual storytelling this book is typically highly recommended.
• Framed Ink: Drawing and Composition for Visual Storytellers - Marcos Mateu-Mestre
I would also recommend checking out used book stores or half price book stores. You would be amazed at how many real gems you could come across.
I've started collecting 'art of' books. Just got the Luca and Coco books. The Taschen Disney classics book is great as well. My dream is to get The Art of Iron Giant, but it's unfortunately hard to find for less than $150 
@Tom-Harshberger is it just artwork? Because I found it in French at my local bookstore in Canada for $ 65
@Blitz55 James Gurney’s books are gold. I was really surprised to fund that he builds so many models so he can better understand how light falls on forms. I thought he was just able to come up and paint it right out of his memory. I started building little models myself since I struggle with compositions out of my imagination. Those are great books.
@Tom-Harshberger I also have a few art of books. Haven’t gotten any in awhile. The last one was Klaus. I also think Iron Giant is one of the greatest underrepresented movies of all time. I would love an Art of Iron Giant book.
@Bill-B My personal favorite is the art of Zootopia. It’s really helpful if you wanna study expressions and stuff 
@Bill-B Oh man James Gurney is my fav. Wore out my Dinotopia book as a kid. He's been doing some fantasy plein air on his IG lately that have been soooo cool.
It's funny, to me, the two best animated movies in the 90's 'golden era' were both non-Disney (Iron Giant and Prince of Egypt). The art on both were incredible. I wish they'd reprint the Iron Giant art of book because it's impossible to get at a reasonable price
@AngelinaKizz Wow! Yes! Just art. I have found the french version online in places at lower prices, but the english versions have become impossible to find. Just looked now, starts at £250 on Ebay.
Growing up, my sister and I shared a copy of this and loved it. Your question just inspired me to order another copy (since I think my sister has ours). 
@Bill-B Right, it's amazing how much we can assume great artists just do out of their head, but to see them use every tool available to them to get it right, and not just make it up can be really eye opening as an artist. Gurney is awesome!
@Tom-Harshberger Iron Giant would be an awesome book to have. I know the feeling a bit, back in college (1999) I had a professor who brought in their copy of The World Of The Dark Crystal book. It was amazing, and out of print and hard to find. I think the cheapest at that time I could find was just under a grand. Luckily a few years later they did a reprint and I got that one.
I may have to keep my eye out for that Iron Giant one as well.
@GabeRobinson That's a great book, I have that one on my shelf as well.
@Bill-B Came here to say JAMES GURNEY, but you beat me to it 
@Bill-B Oh man James Gurney is my fav. Wore out my Dinotopia book as a kid. He's been doing some fantasy plein air on his IG lately that have been soooo cool.
It's funny, to me, the two best animated movies in the 90's 'golden era' were both non-Disney (Iron Giant and Prince of Egypt). The art on both were incredible. I wish they'd reprint the Iron Giant art of book because it's impossible to get at a reasonable price
