Kids aren't always going to make it known that they've seen or heard something either, especially violence or screaming between their parents. Even if they were all treating all the children perfectly at all times (ignoring how we'd seen firsthand on Nick's streams that he wasn't), there's still a vibe among the kids that "this could be redirected/misdirected towards us if we're seen/heard."
They all probably knew a lot more than the Rekietas realize. If the children do make it known that they're aware of the problems, then the parents can either gaslight them into thinking they didn't really see anything, or they admit to the children that the happy marriage is a façade. Both will fuck them up.