DH was brought up with very rigid rules about food. I was expected to eat what I was given, but I don't remember any extremes. DH would be given his dinner for breakfast if he didn't eat it.
I have explained to DH that the way I see things, as adults we have control. If I don't like something, I don't cook it, or I cook an alternative that I do like. E.g. FIL came for dinner today and requested bread and butter pudding. No problem, but I can't stand the texture, I want to vomit. So, I did the pudding and a fruit salad as an alternative. Children don't have that control. They don't buy the food, decide the menu or cook it.
Are children being 'fussy' if they decline to eat something they don't like and have had no input into the menu? I don't think so. They are just exercising choice in a very late stage of proceedings, because that's when they get an input.
It does get easier as they get older. I can now say to DD3 (10) "I'm going to put mushrooms in this dinner, but you can always pick them out'. However, despite loving it myself, I wouldn't make a beef stroganoff as a family dinner. I do make a lovely vegetable strudel - DD2 waxes lyrical at the feta cheese, as DD3 picks it out. Meanwhile, DD3 raves about the vegetables as DD2 is carefully extracting the courgette and aubergine
but they all like some aspect of it, so it stays on the menu.