@Frost-Drive yep, there is no one art style.
For example, look at recent award winners. This year's Caldecott winner was We Are Water Protectors, which was illustrated by Michaela Goade in gorgeous flowing watercolors. (The honors went to Cat Man of Aleppo, Outside In, Me & Mama, and A Place Inside of Me -- all of which were in a different illustration style.) 2020's Caldecott winner was The Undefeated, rendered very realistically by Kadir Nelson. 2019's Caldecott winner was Hello Lighthouse in Sophie Blackall's whimsical style.
Those books could have been illustrated in a different style, but would those stories have been as impactful? Would they have been as successful? Maybe not.
Yes, there is a popular style that you find in a high percentage of books being published -- that's nothing new. But trends change over time. And today you'll also find a ton of other books published that have wildly different illustration styles. It's refreshing, and yes, it is a relief to know!
When I was just starting out illustrating children's books, I also thought that there was a specific "children's book style" that I had to conform to. I could mimic it but those illustrations were stiff or flat -- they weren't ME. So instead I just drew and let whatever came out of me flow onto the page. Turns out, I tend towards more realistic art, and that's okay. My style is not trendy, but I like to think that it's "classic". Nowadays, I focus on telling a story instead of style. That's not saying I've got everything figured out -- I'm still a work in progress! But maybe sharing my meager experience will be helpful.
Keep on drawing and being YOU! ❤️