Let's be honest. No one cares what music I think you should expose your kids to. Like me, you're going to raise them on what you dig, and hope your kids like what you like. Equally the case, there's a LOT of really amazing music and it's impossible to curate all of it for everyone in every way. One of the most important YouTubers in my opinion is Rick Beato: because he's teaching people to be better at listening to their own music. If you can learn to critically listen to the music you already know, then you can be better at choosing which material will impress your kiddos. The linked video is a great video essay about Smells Like Teen Spirit, and breaks down what's actually in the recording-- what set Nirvana apart from other rock and made the music indelible. (Spoiler: there's jazz in there)

If you need to write a letter, you launch your favorite word processor and you make it happen. Essays, poems, stories, reports, cards... ...but what if you needed to do that with music? Until recently, your choice was definitely glitchy, probably expensive, and complicated. Now there's MuseScore3 , and since the update it's been absolutely a joy to use. My source material for learning its features has mostly been a pair of books that used to be in the piano bench in my parents' house when I was growing up. It's freely available and it's developed by the open source community. If you want music to be part of your students' education, it's a definite recommendation. There's nothing else close without spending money. 

Leonard Bernstein was indisputably one of the most important figures in America's part of musical history. He was absolutely a treasure as a performer, composer, conductor, and educator. Decades ago he conducted events called the Concerts for Young People Series. Classical music was presented by a full orchestra, stopped, started, and explained by one of the most capable possible narrators in realtime in front of a packed audience of youths from 4th grade to high school. Leonard Bernstein - Young People's Concerts (In Order)