There is fantastic literature about children's belief in "fantastical beings." It turns out that studying how and when kids decide to believe in the Easter Bunny, Santa Claus, and the Tooth Fairy lets researchers probe how their developing brains make sense of reality. At stake is how the kids measure adult input ("The Easter Bunny is real!") against their nascent sense of how the physical world works (i.e. bunnies are not human sized nor do any animals lay plastic eggs filled with candy).
First, let's establish that toddlers will believe almost anything trusted adults tell them. In one study, experimenters dropped a ball into one of three tubes in front of a two-and-half year old, then told the kids that the ball went into a different tube from what they'd just seen. More than 60 percent of the time, the kids believed what they were told rather than what they'd seen with their own eyes.
Second, belief in fantastical characters leads to the belief in more fantastical characters. So if you teach them about Santa, that could be a gateway drug to the Tooth Fairy and the Easter Bunny
and Ryan Gosling.
As for inculcating those beliefs, it's actually more effective, especially with older kids, to say something like, "Scientists sometimes capture and study Easter Bunnies" as opposed to "I believe in the Easter Bunny." As the kids get closer to double digits, they start to realize that no one has to say, "I believe in this desk." We only affirm that we believe in things that aren't actually real.* So watch out: they get smart about conversational cues before you know it.
But actions actually speak louder than words. In one study, researchers actually made up a new fantastical figure called the Candy Witch, who gives you a toy in exchange for some of your Halloween candy. (My inner child loves and hates this witch!) They found, understandably, that kids who were told that such a being existed and then were actually able to complete the candy-for-toy exchange had a higher level of belief that those who merely heard the tale. The proof of the Tooth Fairy is in the cash under your pillow, am I right?
So, if you're looking to dupe your kid into continuing to believe in Santa and the Easter Bunny, you really should do that whole thing where you put out a plate of cookies and milk for Santa and then you sneak out in the middle of the night and nibble a few of them and drink some of the milk. The calories are worth it! Your kids will retain the delicious fantasy that a fat man with flying reindeer shoots down the chimney to deliver them Star Wars LEGO sets, which is a lot more exciting than the idea that dad bought those toys at Target with a debit card.
But all good things must come to an end, and there is a limited window for the belief in awesome fantastical characters like a giant bunny who lays candy eggs. It's around three years old that kids start to believe in these characters. One study found the average kid stops believing Santa Claus between six and a half and seven years old. So you've only got three, four, maybe five years of actual misguided belief, if you're lucky. Bummer.
There is an upside, though, to the end of the Easter Bunny Phase. It means that your kid is growing up in one of those good ways. His or her brain is learning to trust itself in judging reality, drawing on experience to construct plausible theories for how the world works. And although reality does not deliver delicious confections to celebrate the resurrection of a religious icon, we ultimately do want our kids living in the real world.
*An astute reader points out that we also affirm belief in things that are real, but non-obvious such as the roundness of the Earth.