Somewhat related is an experiment I've been doing with my child, where the only media I've introduced to them (since birth) is in a language other than English

Somewhat related is an experiment I've been doing with my child, where the only media I've introduced to them (since birth) is in a language other than English (we live in the US). Usually this is Swedish or German, which are the languages I know best besides English, but sometimes Spanish, French, Japanese, Korean etc. etc. What I've found is that they have a play/babble language of their own that sounds like a mix of mostly Swedish and German. We talk together in this language at times, too. Sometimes they even have asked me what the English word for an idea/thing they've learned or experienced in German or Swedish. Another time they asked me what "zum Beispiel and till Eksempel" mean! which amazed me because they obviously connected that they both mean the same thing ("for example"). In real life (i.e. not at home watching movies) they can hold conversations with Germans and Swedes, too. At this point they're not truly bilingual, but it's been really fun and interesting to see how much they have learned, and makes available for them in the future, as with deeper study and practice they could be truly multilingual.