Polyamory

I know, right?! It's like those people that wear these weird bands to show to the world that they've been 'taken' or whatever, like, I get it, but please - stop shoving your 'lifestyle' down my throat, ok?! Call me old fashioned, but I think they should keep their kinks to themselves and shouldn't be allowed to wear their weird "wedding rings" in public where children can see them!

OP isn't asking how to introduce their kids to the concept of BDSM or asking to explain how they like being tied up, for fucks sake, they're asking if there are child friendly books to help explain that you can love multiple people. Most monogamous folks introduce their partner to their kids after 6-12 months, so why wouldn't poly folks be able to do the same?

OP - Unfortunately, I think books around LGBTQIA+ and then having a conversation might be the best you're going to get from the quick research I just did. At the very least, your options are slim if you do manage to find anything.

Poly is about more than sex.

Ethical non monogamy is uncommon so there are very few cultural signposts about it. It's reasonable to want to see yourself or your situation reflected in media. Some families have multiple adults in loving relationships simultaneously.

isn't the reason to explain why the kid might have multiple parents in comparison to other children? (sort of like how some children might have only 2 dads, 2 moms, or 2 nonbinary parents) (ah derp they already mentioned this in their post lol)

based on the post it doesn't seem like their intention is to talk about their sex life as you say, that just sounds off and real bizarre