Ahhh, the ol' "is it in-house or not" question.  Thank you, Rich, for bringing this up in terms of the animation area of entertainment.  This inquiry reminds me of a famous quote by probably the most famous writer of all time:  "To in-house or not to in-house, that is the question."  Which, I believe, was changed from its original form (for an apparent reason that will be clear):  "To in-house or out-house, that is the question."  Which is a question of a completely different sort (the sort that we won't be sorting through in the least).  

Of course, Rich, your question has to do with a specific area of the entertainment industry, namely that of animation, which I've had only some experience with.  There may be special "rules" when it comes to animation, but, as far as I've experienced my some experience, I haven't seen any.  The truth is that producers, story editors, and all down the chain like to hire those people whom they have hired before and like their work.  It's that simple.  Before you cry, "Nepotism!!  Down with the king and all that he stands for!" consider that, if you were in a hiring position, that you, too, might very well be inclined to want to hire those you already know, those you like working with, those whose work you appreciate.  In other words:  Your friends.  Or at least those whom you can stand the sight of.

But here's where you come in as a new writer to a particular "fold."  No matter how "in-house" (you can read:  "incestuous" if you like Freud) a company may want to be, that company is going to need new material, fresh, well-crafted material -- and they are not always going to be able to find it in their blocked out gene pool.  Without "fresh blood" (and I'm not implying that any vampire-like activity occurs in the entertainment field, that producers and studio executives would ever really "suck the very blood and marrow" out of a writer until he was merely a husk of his former, creative and energized self.  I'd never say that.  Never.), a production company, be it in animation or features or whatever, cannot continue to thrive.

As to your specific question, I urge you to ask a different one, which goes like this:

Why wouldn't an animation company be open to you submitting an original holiday script about children and family?

Not to get too carried away here, Rich, but do you see the importance of how you pose your question?  Your original one begs for a negative response.  I don't think you would want to call an animation company and ask them if they'd consider looking at your script.  Better would be to call the company and let them know that you've written an original, family/holiday script, which you would like them to take a look at.  Do you see the difference between the two approaches?

On a personal note, I did get some script ideas into a major animation studio because a colleague worked at the company and opened a door for me.  That's always nice when that happens.  But who is to say that you can't "open your own door"?  I'm not going to start into a lecture about persistence (I don't have the persistence to), but all I can say is that, if you believe in your animation screenplay, Rich, then let that belief translate into taking action to let others know about it.  Make it part of your routine.  Along with taking action, visualization can be a helpful device.  Here's a good visualization (that is if you like to visualize.  If you get stuck on that part, just visualize yourself enjoying visualizing.):

Picture yourself on a boat on a river with tangerine trees and -- No, that's not the one.  Oh, yes... (And this one is specifically tailored to Rich's situation):

Picture/visualize that there is an animation company out there that is looking for a wonderful holiday script, exactly the kind that you have written.  It's actually looking for your script, so to speak.  Continue your imaging (if you prefer to) and see yourself contacting this company, somehow connecting with it, letting it know about what you have to offer, and the company responding favorably.  You can even expand the visualization and see the company purchasing your animation script for the amount of money you desire to have in your little animation-writing hands.

They say (whoever "they" are) that visualization is a powerful tool that, when used properly, can bring about excellent results.  I've used it many times and found it to be very helpful.  I mean, even at this moment, I'm visualizing that I'm coming to the end of this article and finishing this paragraph.

Wow.  It really works.

DcH