I'm not into pandering to kids and their dislikes when half the worlds' children can't even get enough to eat every day. I cooked dinner and put it on the table. If they didn't like it they got themselves bread and butter.
Edit: Sorry - that sounded snappy. Just don't worry too much about food and kids. Fussy eaters are just reflecting their parents' anxieties about food.
I don't pander to my kids with regards to food. If they don't eat it, then they go hungry - no bread and butter, because they would happily choose that as the option. But it doesn't stop them being fussy. Never stopped me being a fussy child either.
Absolute bull about them just reflecting their parents anxieties about food though. Children are biologically programed to be fussy. It is an evolutionary, protective mechanism. They are programed to dislike most vegies and anything that isn't sweet. This is believed to be to help them avoiding poisionious things, which naturally tend to be bitter. Kids can actually physically feel like gagging when consuming foods they do not like. Our taste buds and our reactions to food change as we age.
As for a genuine dislike of something (ie, fish) I wouldn't stress too much. If I felt like being accomodating I might prepare an option of fish or chicken for people to choose from, or If not feeling so accomodating, I might simply make them eat everything else served with the meal (ie, the vege, or salad, etc), but not push the fish issue.
If they are eating a wide variety of healthy foods which include other healthy oils, it shouldn't matter too much if they are not eating fish or other seafood. Other foods such as avocardo, nuts, oats, etc all contain good 'brain foods'. As well as ensure any margarines you use contain omega's and using healthy oils in you cooking.