Hrm... I'd say try to raise them, well, to think rationally. If you actually do decide to give them a "easy obstacle to train on", make sure you're otherwise getting them thinking rationally, and if they ever start calling you on the inconsistancy, or get suspicious, don't try to "cheat" or otherwise discourage such. Heck, maybe the correct thing is to do such, but to right way admit it when called on it, no hesitation at all.
Or alternately, if they ask "if santa's real", explicitly suggest it to them as an exercise, as something for them to try to figure out a way to actually test or otherwise determine.
Related on OB: Lying to Kids The Third Alternative
My wife and I are planning to have kids, so of course we've been going through the usual sorts of debates regarding upbringing. We wondered briefly, will we raise our children as atheists? It's kindof a cruel experiment, as folks tend to use their own experiences to guide raising children, and both of us were raised Catholic. Nonetheless, it was fairly well settled after about 5 minutes of dialogue that atheist was the way to go.
Then we had the related discussion of whether to teach our children about Santa Claus. After hours of debate, we decided we'd both have to think on the question some more. It's still been an open question for years now.
Should we teach kids that Santa Claus exists? This isn't a new question, by any means. But it's now motivated by this thread about rationalist origin stories. Note that many of the posters mark the 'rationalist awakening' as the time they realized God doesn't exist. The shock that everybody, including their parents, were wrong and/or lying to them was enough to motivate them to pursue rationality and truth.
If those same children were never taught about God, Santa Claus, and other falsehoods, would they have become rationalists, or would they have contented themselves with playing better video games? If the child never realized there's no Santa Claus, would we have a reason to say, "You're growing up and I'm proud of you"?