If I were to write a childrens book, how would I write it?

[Flynn]

You are wrong on both accounts, unfortunately.
It all depends on how old the child is - the style and vocabulary must be tailored specially to the child's age.
The style of book also depends. A picture book would have few words; letting the vibrant pictures doing the talking. A novel for small children wouldn't read like a normal novel, but with simpler sentences and words.
You need to envision how old your target audience is, because an average novel would be targeted at at youngest an eleven year old, whereas a book with phrases such as "That's right, it's behind the curtain!" are more for a two to five year old. Only then can you know how advanced the language in the book will be.