Even if it portrays fiction, I think that this should be limited to adult audience still.
Social media, mass media and other types of media can easily be accessed by children these days. If the parents wont be careful and watchful with their kids, they could trigger their own curiosity that will lead them to watch porn.
It serves as a reminder.
I agree. It's always up to the parents regarding how they'd like to limit and/or prevent these sort of things from happening inside they're homes. Granted that these parents are fully aware and are techy enough at least, to figure out what's really best to do, in order to prevent these sort of things to be viewed accidentally by their children.
This is more a remainder to parent that keep an eye on the kid and should be always open to speak to them at appropriate age. Kids are smart and will find some or other way to watch it. So, this is what the purpose of the ads is that also for KID to be aware about it and if caught it would be like red faced like that kid in the ad.