Hi Cardigan,
Our situation is almost identical. I'm American (and Armenian) and my DH is German, and he wasn't so sure that he could manage to speak to our now 2 year old exclusively in German since he lived in the UK for so long and is now in the US. However, from day 1 of our son's birth, he spoke ONLY in German, which is amazing! I'm very proud of him (especially because my DH is not at all a verbal person!)
I agree with the other posters, who've offered excellent and do-able advice. My IL's have been wonderful about providing us with age-appropriate and beautiful music and books in German. For the first year and a half, I played German music 3 times daily, and only recently introduced him to English radio (though I'd sing to him in English). When my son wasn't yet talking, I read some of his German books, though now that he's a little parrot, he knows that I prefer that Daddy read to him from those books. Of course his English is much stronger than his German at the moment, but there are some things he only says in German. Also, I'm confident that he will be speaking even more German after our visit to the IL's in June as he will be immersed in the language (and I will try to talk less to minimize the English!)
He will soon have a little cousin in Germany so I think exposure to other children who don't speak English will be a plus.
Since we are in NYC, I've found German schools, camps, and classes, and send him to one short class once a week. He can now sing (ahem, in the way that a 2 year old can) the classic German songs that I played from the start because he's now hearing them in a new context. (If you want a starter list, feel free to send me a message and I'll send you some titles).
We are a tv-free family, though we purchased a few classic children's cartoons from Germany (Die Maus and Sandman). Not sure when I'll introduce them to him as I would love for him to be enthusiastic about his minority language, though don't want him to be dependent on media just yet. You could also find music or cartoon clips on YouTube.
DH would be delighted and motivated by your enthusiasm, especially if you get your IL's to encourage him further!
Ps. German toys are amazing, so make sure to get as many Haba toys that you can find if you go on any visits, though they are heavy to carry back!
And have a WONDERFUL pregnancy!!!
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