For a less emotive response, let us substitute Klingon with Norwegian, outside of Norway.
It is not child abuse to bring up your kid to speak only Norwegian in Australia. As another respondent said, if they arrive at primary school with no English, they will pick up English pretty quickly at school. As is the case for countless immigrant kids. And if the kids socialize at all outside the home, or watch TV, they will have picked up English anyway.
So the issue is not depriving a child with access to English.
Let’s substitute Norwegian with Esperanto, or Latin. There are, after all, something like 1000 native speakers of Esperanto. Have these kids been subjected to child abuse?
I mean, sure, their peers will think it’s weird and they will make fun of them. Their peers also made fun of the immigrant kids who ate weird food and looked different. And by all accounts, kids brought up speaking Esperanto end up perfectly well adjusted, although not many of them retain an interest in the language. Peer pressure is effective, after all.
And as I have said in a different answer, I’ve cyberstalked the kid who was brought up to speak Klingon (and lost interest), and I found a picture of him as a teenager in a mosh pit. I’m not worried about his long-term socialisation.
So what in this scenario makes people so aghast at Klingon? I’ve heard the child abuse accusation from professional linguists too. But a kid is hardly going to sustain brain damage from a language that violates a couple of phonological universals. No one should be taking Chomsky that seriously. If a kid can deal with a pidgin as linguistic input, and come up with a creole, they can certainly deal with Klingon. Not to mention, any Klingon that a parent would produce day to day would not be all that alien.
The only rationale for a claim of child abuse would be fear of difference and fear of unconventionality. Hippies have done far worse to kids.