Hi Carla. Great question. A child learns and remembers a new word on ONE exposure. . That’s amazing. But, we adults don’t have this capacity. For me, flashcards are worthless. Songs are only minimally effective, and reading helps,  but you really need a context to remember a word. For some odd reason I can’t explain, hearing a native speaker speak the word helps me remember it much better than reading it. I’ll never forget I was in Germany 2 years ago but there was a word I didnt know (although I speak German, I’m always building my vocabulary, like we do in our native languages.) I was watching a YouTube video, in German, and a Lufthansa pilot was describing, in German, how he was approaching a landing at San Francisco, and the tower was setting his flight up for landing, and he used the expression „wie ein Trichter.“ This was in the context of other flights lining up.  I knew what „wie ein“ meant („like a“ ) but I hadn’t heard the word „Trichter.“. So, I asked my German friend what a Trichter was. We were in her kitchen. She said nothing, but turned around, opened up a drawer in her kitchen, pulled out a funnel, and slapped it down right in front of me without saying a word. From that moment on I learned the German word for „funnel“ and I’ve never forgotten it for a second ever since.