The internet is a mysterious place. There's an endless wealth of knowledge available, and we spend a good amount of time watching pandas sneeze. At one point, people were flinging cheese slices at their dogs as part of a social media challenge that had some hilarious results. Now, that's morphed into throwing cheese slices at kids.
It's not worth trying to find a more complex explanation. You're not likely to find a satisfying answer. It's clearly just for a laugh, even if the joke is at the expense of toddlers. The challenge falls into the same category of the demonstrably mean Jimmy Kimmel Halloween challenge. It makes you cringe a little. Though, you're probably laughing at the same time.
Fortunately, everyone loves cheese. Getting cheese thrown at you is just getting a little free cheese.
Here are some of the cheese tosses, which were originally collected in a surprisingly extensive Twitter thread. (That thread can no longer be seen because the original poster deleted their post. The video wasn't theirs and originated on Facebook, according to a note on the user's Twitter feed.)
Who knew so many people loved throwing cheese?