As a father, I make sure that my son only sees things that I believe are age appropriate for him. I'm his babysitter, not Netflix on demand. That said, I have occasionally made bad estimations of what would be contained in something, and I shoulder the burden of giving the explanation.
It would be different if, say, Dora the Explorer suddenly started talking about sexing up Boots or whatever, because in that case, I'd feel that I was expecting exactly what I've watched 80 episodes of, and taking that kind of detour is something I should reasonably expect won't happen. But if I say, "I know just what's in the description of this show" and I don't search it online and just rubber stamp it, I should be prepared for anything.
I have different levels of comfort with a variety of topics than the MPAA or whoever has, for instance, I don't try to pretend that "fuck" is a word that we only use in the most extreme situations. Sexual situations happen in reality, I don't mind if he sees a few boobs. But I don't want to see any kind of implied or on camera drug use, even weed, in things I let my son see,.