This is particularly prevalent amongst trans people on twitter (where I see it used a lot) you see a lot of people using this emoji under for example a powerful looking selfie of someone who appears dominant, as a playful offer of submission.
There’s lots of emojis that the culture has given alternate meanings to, for example the peach and the eggplant.
You could ask “how would I explain this to a child” to anything adults talk about that is sexual in nature. Usually the answer is “don’t.”
I don’t think TFA was written for children and the author wanted to include this common internet meme in to their article title.
Imagine you drop your finger randomly on a word. How can you find the start of the sentence it's in?
(After this, if the child were familiar with binary, I'd show the actual representation of UTF-8, perhaps colour-coded. It's really quite intuitive. No need to go for the abstract straight away: if the child can generalise, they can generalise, and if not, there's no point making it artificially confusing.)
You wouldn't. Just like you probably wouldn't explain the sexual meanings behind the eggplant or peach emojis to a child.
Not sure why this needs to be a consideration. If you're writing for an audience that includes children, sure, use child-friendly terms and concepts. If you don't care about including children in your readership, go nuts.
Granted, I don't think everyone needs to be prudish, such that this is a bit of a tempest in a teapot. But it is very different than claiming that explicitly sexual reframing of other items is the same thing.
And I'm a little concerned why not knowing about something that seems like an esoteric piece of fetish-related in-group communication implies that I don't hang out with queer people? Is there an expectation that in order to hang out with people belonging to some group, I need to learn specific lingo regarding that group's sexual power dynamics?
If it helps any, its official name is U+1F97A, FACE WITH PLEADING EYES.