My first thought of course was to say it isn't, but for middle grade (older elementary school and preteen) fiction, at least, there are subtle differences. One of them that occurred to me as the conversation went on: to write for kids, you need to see kids as characters first, and children second.
And then I got to thinking of pmsamphire's post on how not to do an American accent. He talks about how you should never write an Elf, for instance, but only a character who is an elf.
And I think that's it exactly: in kids' fiction--and teen and adult fiction with younger characters in it, too--you need to never write a Child, only characters who are children.
I've been realizing the past few years that adults often not only have different writing protocols for child characters, but also different reading protocols. I forget where Neil Gaiman said that adults find Coraline terrifying, because they see a child in peril; but kids reading it just see someone having an adventure. I've seen, too, times when adult readers will either see a child character and assume a sort of cheap emotional manipulation--there's a child here, the story must be trying to make me feel scared or sorry for her; or else will interpret stories that seem quite dark as being "cute" simply because children are present.
It's easy to forget, when writing in a kid POV, that childhood can seem like a foreign country to adults. Often enough, out in the world, something or other will remind me that while I write in that country, I don't live there anymore either--and that fact will feel like a victory or a loss, depending.
But as adult writers and readers we have an advantage. We've never been to Elfland (or I haven't, and if you have, why haven't you told me?) but being a kid--we all lived there, once. We have memory and the kid-in-us and the kids who are part of our day-to-day lives to remind us what being a kid felt like. Not that remembering is always easy or painless, or that we always remember as well as we'd like even so--but that remembering is a crucial part, I think, of not talking down to kids in kids' books; and of not writing children as Other, in any books.
I also like to think of it as a way of honoring kid-that-I-was--who went through an awful lot, really, to get me here to my adult life.