a lot more competitive than I look

I gave

1 teeny Métis sash woven with crewel wool on a rigid heddle loom, sized for an 18" doll such as Our Generation or American Girl

In exchange for

1 out-of-tune hammered dulcimer

WHAT IS MY LIFE. I said "Yeah, if I were to seriously learn an instrument it would be the hammered dulcimer, but they're impossible to find on a budget," and the person I was talking to said, "I have a hammered dulcimer I don't use."

(I don't have enough fingers to play a lot of the instruments I want to, and my formative music instruction was in Orff ensembles, so it's the best overlap between what I'm capable of and what kind of music I want to make)

okay

Well, one famous thing about the Spanish Civil War is the International Brigades: volunteers, largely in highly varied shades of leftism, from all over Europe and the world who showed up to fight the fascists. (Anglophone readers may recall Hemingway's For Whom the Bell Tolls and Orwell's Homage to Catalonia.) So alongside the songs in Spanish and Catalan that came out of or get associated with the war, there are many International Brigades songs in English, German (yes, lots of German communists and other anti-fascists in the '30s went off to fight fascism where it seemed vulnerable), Italian (ditto), French, and this collection appears to have at least one each in Czech, Polish, Hungarian, and one that's attributed to "Yugoslavia" but I do not have the South Slavic expertise to tell you what language it is in. Not a song, but I have seen a poster specifically recruiting Esperantist volunteers. Very multilingual environment already.

And then... the Spanish Republic lost. The fascists won. The songs went pretty quiet in Spain. But the international volunteers that survived and went home kept singing them. And so did one of their sympathizers: Pete Seeger, whose recording Songs of the Lincoln Brigade introduced many of them to a broader audience. On that album you can hear Seeger singing songs in both English and Spanish:

Or how about the German communist volunteer and singer Ernst Busch doing the "Song of the United Front" in Spanish, English, French, and German:

(oh gosh my YouTube music recommendations are going to be so communist for a bit. That's all right, they've been quite Jacobite lately so that will balance it out.)

Of course, fascism in Spain didn't last forever, and today many singers and groups in Spain do perform and record the same songs. ... Including the International Brigade ones. (Unfortunately I can't track it down, so this may not be true to any extent at all, but I have read a remark somewhere [possibly in someone's liner notes?] that after the death of Franco, young people in Spain rediscovered these songs specifically through Pete Seeger's recordings...!)

So you can find the Catalan "Quartet Brossa" singing the Italian Bella Ciao:

Or the evidently Spanish-speaking "Coro Popular Jabalón" doing their best American English in the soldiers-complaint song "Quartermaster Store":

On the same album they have a song in Basque:

And so on and so on.

(You may have noticed Spain's minority languages, including Catalan and Basque, making a good showing here: that's no accident, those were evidently quite republican areas, as will not surprise you if you know anything about Franco's language policy.)

Anyway those are the main historical reasons I'm aware of why music from and about Spanish Civil War is so multilingual. Obviously my original claim that "almost nobody is ever singing in their native language" had an element of hyperbole - the Americans do sing songs in English (as do the Irish), the Spanish in Spanish, the Germans in German, and of course the Catalans in Catalan. But if you look for Spanish Civil War music, many of the "standards" you'll find are International Brigades songs, many others are Catalan as well as Spanish, so no matter what your native language is you will have plenty of songs that aren't in it.

And apparently you sing them anyway. Because, at least for the people making these records, it seems it's not about where you're from, or even whether your accent is any good, it's about standing side by side.

Young kids are also a lot more socially aware than people give them credit for. Young children are perfectly aware that adults don't take them seriously. They know when their parents don't actually like them. They listen and remember when adults talk about them while they're in the room. Kids will develop basic abilities to charm etc. from babyhood and will begin experimenting with social norms and concepts of deception, appropriate information, and acceptable language and attitudes in toddlerhood. By the time a kid is five or six, they have solid social strategies for relating to adults and separate ones fr relating to their peers, that they'll continue to refine for the rest of their lives. They will also say completely off the wall shit because they don't have the context to know what is and isn't considered super fucked up yet.

By the time a kid is eight or nine, their main difference from adults is in experience, interests, and ability for long-term focus. An eight year old can think as intelligently and coherently as a thirty year old, they just have less experience and information to draw from, and are likely interested in very different things. They're also likely still slightly hamstrung by vocabulary and literacy, though much less so than a younger kid.