Yeah... $190k sounds a lot except in any HCOL area (SF, NY, LA, Seattle, heck even Portland has skyrocketed) it's going to feel very tight with three kids.
Plenty of people do. $190k's just this ridiculous "from first principles" logic game on how much money you need to "survive" there, but it really means "not panic over money or going hungry and bank a little in an emergency fund and a retirement account" level of living, and not "If I eat ramen for a week I can afford the concert ticket" level of subsistence.
But is 120k at least somewhat comfortable for a single person? These different levels you described really hit different as you age. Yeah I could be ramen level but if the option is to not be ramen level at 120k elsewhere then moving to LA is not worth it but if there is a minimum level of comfort then other things make it worth making the move.
LA and the surrounding area isn't cheap to live in. It really all depends on what you do with your money and how lavishly you want to live but I'd say $120k is actually quite reasonable if you're able to live reasonably. Given the choice of $120k in LA or $120k elsewhere, I'm not going to lie, the $120k is going to go further elsewhere (except for, like, SF or New York), but then you're not in LA.
I also don't mean to impugn ramen either, as LA's got some really really good ramen restaurants. It all comes down to if you want to or not. LA's got a lot to offer but it's not for everybody.
I make 150k in LA, with 3 kids, and am the primary income earner. It kinda depends on where you live, LA is a big place with a hugely varying cost of living. I live in the suburbs and it's enough. If I lived in Venice I couldn't afford rent.