First, you will need to ask yourself how important it is that your child has fish. If you really want them to eat it, you may have to be willing to give way on other issues such as how it is prepared. There are a variety of frozen food companies that present fish in stick, and even fish shapes. But these are wrapped in crumbs, and sometimes partly deep friend before you cook them in the oven. This might not be ideal, but if they will eat it, and get the taste of fish, it may open the door to other, and better choices.
The other options are mostly those that appeal to taste. An excellent way of serving fish is in a sauce. A fillet of haddock can be baked quite nicely with just mushroom or another creamed soup poured over it. If you cut off a child size portion, you can even decorate it with some curls of celery for hair, and sliced pickles for eyes before serving. Use your imagination here.
A lot of children love cheese. Bake your fish until it’s half done and then cover it in shredded cheddar cheese. Not only do they absolutely get the taste they like, but the extra protein that cheese offers them.