TOD
First song ever heard would be "Let's Get Together", since we saw The Parent Trap when it was released. But I didn't have any idea who wrote the thing. Likewise, In Search of the Castaways and The Sword in the Stone which followed.
It wasn't until Mary Poppins that my consciousness was, um, expanded and I learned their names. They were plastered on everything, of course, including the LP and the "complete musical score", both of which I immediately bought and treasured. And that was it. Once Mary Poppins exploded on the scene, there was no more "not knowing" the Sherman Brothers.
(Sadly, that book of music went missing along with several other "real" scores, at some point during my college years. I eventually replaced it on eBay, but while it's the "same", I can tell by the look and feel of the paper cover that it's of a later printing. Those first ones are very hard to find.)