@makenzifox,
Any writer, regardless of calling, needs to learn how to write. So start writing. Good stuff, bad stuff, completely off-topic stuff. Just start writing.
Your early work will stink. I can pretty much guarantee that. But writing ability does not spring out of you, fully formed, without work. It is a skill that you will need to master, to learn how to write compelling prose. And writing for children is not simpler. It is not a matter of dumbing down your 'regular' writing. It is appealing to a very different type of audience. I also strongly encourage you to read. Since you want to write a children's book (and recognize that writing for preschoolers is far different from writing for tweens), I urge you to read children's books. Read classics, like
The Wind in the Willows and
Charlotte's Web. But you should also read the top sellers on the
NY Times Bestseller List and look at their lists for children's books (which they divide into chapter, pictures, etc.). Tastes have changed, and what appeals has changed over time. And don't forget that the people who buy children's books are almost always adults.
Even if you do not care about sales (and you should, as that will be how you make a living; even people called to the Lord's work have to buy groceries), they are an indicator of audience and popularity. If you want more than just your immediate family to read your work, you need to understand the marketplace.
I further encourage you to check out the
NaNoWriMo Young Writers' Program as they help teens like you write books every year.
Best of luck to you in your endeavor. Writing is a fun and creative outlet.