My kids will take the cod liver oil (orange flavoured) if they have some milk or kefir to chase it with. I personally find the orange flavour disgusting, really fishy. But I actually like the cinnamon flavour! Not fishy at all to me. Whereas the rest of the family loathes it. So I think it's a matter of finding the type that works for you. Such a shame they don't sell little taster packs. I would have started using it years ago but I was scared to spend that much on something the kids would refuse.
Butter oil is another matter. We all hate that! Even mixed with butter and spread on stuff. So I've been making it into little chocolate truffles, each with about a quarter teaspoon in. And now they fight to take it! I have not problem with them having a little dark chocolate every day, especially with the HVBO in it.