This is, of course, because the impulse to protect children from harm often gets corrupted by the emergence of the monster called the self. It is not enough to be vigilant against threats. There must also be the cringing and remorseful admission that parents always know better because no person alive can escape that little killer called the ego. One would have to be one of Asimov's positronic robots motivated by his mythic Three Laws to escape the need to have one's ego stroked and since Elly is all too human, she has to guard her idiot children from all the bad things that they want.
The problem is that she cannot eventually avoid hearing herself ape Marge Simpson when she confidently stated that everything she didn't see the point of must be banned without any sort of leniency. At some point, her mentally editing what her children say to change brand names to 'sugar cereal' or 'junk food' and band names to 'headache music' is going to run into the brick wall of having to admit that she's turned into her mother and that, no, that isn't a good thing. It would be like having to face the fact that she can't lecture her children into erasing the stuff she's ashamed of having done when she was a kid.