It seems weird to me that a lot of parents (I'm from USA, unsure if this happens elsewhere) tell their kids that Santa is a real guy who constantly monitors their behavior and then rewards/punishes them accordingly. Some parents I've seen go to really elaborate lengths to strengthen the lie, like, letters to and from Santa, cosplay, the elf on a shelf thing, etc.
Has this always been a thing? If so why? It seems like a lot of work that'll make it so your kid is less thankful to you about Xmas gifts, and they'll feel betrayed in the long-term when they find out, so why do that at all??
Both Peter Gainsford (http://kiwihellenist.blogspot.com/2018/12/concerning-yule.html) and Spencer McDaniel (https://talesoftimesforgotten.com/2019/12/07/the-long-strange-fascinating-history-of-santa-claus/) have written blogposts on the origins of Santa that might interest you.
The short form is: "Santa went through several phases, starting out as St Nicholas with no connection to Christmas, then metamorphosing into the Christkind and Sinterklaas, before re-coalescing into Santa." (see Gainsford)
The Santa we encounter today bears traces of each of these phases (e.g. that of the gift-bearing saint) and is ultimately associated with Christmas. The custom itself, i.e. attributing gifts to Santa, can be traced to the mid-16th century at the latest, though still to Santa's predecessors.
For example, Martin Luther writes: "Just as little children are taught that if they fast and pray and spread out their garments at night, the Christkind or St. Nicholas will give them presents. But if they do not pray do not give them presents or give them a rod or a horse apple."
One can see quite clearly from the quotation that there is already a strong underlying "pedagogical" intention here, even if religious connotations are of course still present.