How late are the extracurricular activities? I'm not American, but at home we would just eat all together after, e.g. around 9 p.m. and if they were later in the evening, we would just eat a bit earlier, like 7.
I think many Americans would look at you like you were nuts if you suggested regularly eating dinner around 9pm. I'd say 5-7pm is the most common here. Often when trips to Europe come up, the discussion is about how you can't get dinner at 5pm because the restaurants aren't open. Although my last few trips to Europe I noticed there are more restaurant choices in touristy areas that open early just to get the American's business. I've also noticed it's better to wait and eat when the locals do. Some of the worst Italian food I've ever had was in Milan at a touristy restaurant, and some of the best was in the same town at a place that a local recommended outside of the tourist areas.
I think you have found the heart of this issue. As a French I wasn’t understanding the points being made about extracurricular activities but here a 7pm dinner is considered early and most people will eat around 8 up to 9. To be fair few people leave work before 6:30pm and being home before 7:30pm would be exceptional.
My beef with US supermarkets the only time I went there is how poor is the quality to price ratio is particularly for vegetables. Generally speaking you could shift every thing one price band compared to France.
When I was in school, we ate as a family when schedule allowed. For most of primary school, sports were done in time for dinner. Music lessons were usually 1-2/week and often after dinner (instructor had a day job too). In high school, dinners as a while family were less frequent, but whoever was home would eat together. Same for the short time I lived at home after college - dinner was around 6pm and Mom expected me to let her know if I wouldn’t be home (default assumption was I’d eat with Mom & Dad since I was living there).