"Banal" would mean "dull, uninteresting, and generally pointless". I think you're looking for something more like "malicious":
The worst thing about those malicious videos of children doing terrible things to strangers, is that their notoriety might inspire other children to do the same.
Other possibilities: nasty, immoral, vicious, mischievous, awful, heinous, ugly, vile, depraved, offensive, disgusting and various others.
Each of these can have a different nuance, but if you explain exactly what you want to say, I might be able to point to one of them as the most appropriate -- for example, do you want to focus more on the immorality of the acts show in the videos, or on how they offend you personally?
[Edit] As you might expect there is no single word to describe everything you want to say. However you might try some combination of these:
irresponsible (adj): not thinking carefully enough or not caring about what might result from actions taken
frivolous (adj): (of people) behaving in a silly and foolish way, or (of activities or objects) silly or unimportant:
infamous (adj): well known for something bad; notorious:
seductive (adj): making you want to do, have, or believe something, because of seeming attractive:
While these videos might seem like so much harmless frivolity, they encourage irresponsible behavior among young people who have yet to develop the moral compass to distinguish the malicious from the benign.