I have never tried sushi, never really even thought about it, I am not a great fan of the concept. But lately, my daughter keeps mentioning it and how much she'd like to try it, so it seems that I can't avoid it for much longer...
I had no idea that yellowfin tuna is an endangered species. Actually, when we last visited a gourmet restaurant here and I ordered that dish, the waiter was "regretful to announce that the dish is not currently served because the fishing season is off for yellowfins" -- now, I know!
As for eating out, my son is like a machine and eats like a grown man - in fact, like a old man, he prefers all the traditional foods that other kids hate, and he dislikes pizzas, toasts, sandwiches, etc; he is only 8 for heaven's sake! My daughter on the other hand is the exact opposite, she examines every discoloration and herb on her plate, picking it all carefully, putting aside anything that looks "suspicious" in her mind; she only likes gourmet dishes (the most expensive ones usually) with no questions asked. So, I can relate to your experience more or less, good to hear you all had a good time there.
I am no expert on tuna but I have heard that there are restrictions on yellowfin and bluefin, while skipjack is ok - apparently, again its only hearsay and i haven't really checked up on it. not even the otherwise mandatory quick websearch. My wife and I went to Japan on our honeymoon more than 20 years ago and since then (and actually also before, which is why we chose japan) I have loved everything japanese. There is much more to japanese cuisine than sushi, but sushi is the most readily available outside japan.
In Denmark we have a sushi/yakitori crossover called sticks and sushi which is a very nice compromise if part of the family is not too fond of raw fish on rice. yakitori is grilled food and much more palatable for most kids than sushi, while still retaining the overall aesthetic which appeal to so many people.
I ate like an old person when I was young as well @nyarlathotep loving things like liver and onions, pate', all kinds of fish (raw and cooked). I think it's because I was raised by very old parents and was often at adult functions so the food was just, well, adult and I was used to it. I HATED the stuff other kids ate especially tinned food like tinned spaghetti, no thanks.
We sort of create our palette at an early age I suppose?