While most people agree that it is bad practice to lie to children, most parents will make an exception when it comes to Santa Claus.
Some oppose the Santa myth on religious grounds. Others dread the day of revelation.
Others, however, hope to recreate some childhood magic for their own youngsters.
A common concern is that lying ultimately will erode children's trust in their parents. When your child begins to question Santa's existence, you could have an honest conversation with them about why you supported them in their belief, citing perhaps the enjoyment genuine belief produces.
It's always possible that they might resent the deception or question your judgment in other areas but it's unlikely your child will hold it against you for too long.
(If you're really worried about this you can always be truthful with your child from the start and engage in pretend play: "Let's pretend Santa is real and leave some cookies out for him!")
Another potential problem that is sometimes raised is that encouraging belief in Santa could make it difficult for children to distinguish between fantasy and reality - possibly delaying their cognitive development.
But research suggests that the ability to differentiate fact from fiction actually starts early in childhood and increases with age.
In fact, some studies suggest that children with rich fantasy lives may actually be better at identifying the boundaries between fantasy and reality. For example, many cognitively normal children develop imaginary companions and naturally outgrow them.
Arguments in favour
There are two main arguments: One is the pleasure they get from the idea of the kindly old man with the big beard and sack of presents. The second is that they behave better because they think they have to be good in order to secure the best returns.
Any short-term benefit from believing in Santa vanishes when children stop believing in him. To achieve real behavioural change, children must learn by reflecting on their own self-motivated behaviour. Encouraging them to believe in Santa might temporarily make it harder for them to do so.
There's no evidence that children are harmed in either case. Parents shouldn't be overly worried about the repercussions of believing in Santa - children are not completely credulous.
The key task for parents is managing the likely disappointment that comes when their children eventually grasp the truth.
Jared Piazza is a lecturer in Moral Psychology at Lancaster University