The contest policies and site policies are one thing on this matter; let me get into my own personal viewpoint.
First of all, I think any parent who's letting their five-year-old kid go online by themselves is quite irresponsible. It's so irresponsible, in fact, that I think it barely happens. I'm assuming that any kid who watches this will be at least nine or ten.
Second of all, I did put a content warning there, and even made a version which removed three of the stronger swear words. I know that some people are offended by blasphemous language, but they constitute a relatively small part of my audience. Being a secular humanist myself, it would feel awkward to censor according to religious injunctions.
Lastly, I've never been a big believer in the idea that kids automatically emulate what they see or hear in the media. Knowing a swear word because you heard it somewhere is one thing, using it all the time is another. When I was nine, I knew the standard repertoire of dirty words, but still didn't use them in conversation at all. Especially when you're older, it's quite possible to see attitudes in the media that are radically different from your own, and still not be affected by them.
If you personally find the content distasteful, you don't have to watch it, but there is no case for shielding everyone against it.
I'd be interested to know what your stance is on violence in brickfilms. It seems like so many brickfilms have levels of violence that, by your reasoning, would be quite dangerous for young children.