> if you asked me the words for 'cedar', 'robin', 'pond', or 'linen' I would be struck dumb. And yet presumably every ten year old I walk past in the street would know those words as comfortably as I knew them in English as a ten year old in England.

Indeed. I'm American but my family has spoken German in the USA uninterrupted for 200 years. I speak German with my kids. But there's a children's song called Alle Vögel sind schon da and another called die Vogelhochzeit that I listen to with my kids, and it's just a litany of bird species I do not know but, being in a kid's song, I assume means they are common words for German kids.

When I look them up, the English words are ones I've heard and know from context are birds, but I couldn't tell you what they are like, and I would never use the word in English when asked about birds. My go-tos would be mockingbird, cardinal, hummingbird...ones I see in my backyard and have seen my entire life.