Well, you would be surprised how much historical writing you are locked out of by not being able to read Latin. Not from antiquity, but from the fall of rome up until the turn of the previous century, Latin was the language. A tiny fraction of what's been written in Latin is available in any vernacular. By not reading Latin, you're locked out almost all western pre-modern writing.
> Plato complained that "children today are not learning the things that they should"
Where does he say this? This seems an incredibly uncharacteristic sentiment coming from Plato. If nothing else because his mentor Socrates was sentenced to death for corrupting the youth, and almost all extant writing from Plato deals with Socrates' legacy. When Socratres isn't harassing rulers and generals, he's typically portrayed hanging out with the youth in Plato's writing.
Closest thing I'm aware is a section of The Republic. The section, a hypothetical aside really, deals with the horrors of Athenian democracy (the same that killed Socrates), where fathers fear their sons and children are said to think themselves equals to their parents.