Earlier quoted context omitted.
"Children aren't typically the family index case during lockdown" doesn't really tell us much about non-lockdown spread.
But all the evidence from European countries tells us a lot about non-lockdown spread following a proper lockdown.
Which the US refuses to do.
It's like we're the kid in school who refused to do their work, then has a tempter-tantrum because they have to forgo recess. And much of the EU (and Taiwan, Singapore, HK, etc) are the nerdy kid who finished early and now get to spend the afternoon doing something fun.