I never eat seafood, not sure what the fuss is about. Partner won't either, so only Miss 10 eats it as her dad feeds her nothing but fish when she visits him. Visiting weekends always involved her going away, not having a bath, and coming back reeking of strong-smelling fish. I have thrown out maybe 30kg of enormous hideous stinky fish fillets he gave me for her, amazing how it takes someone over a year of telling them "I don't eat fish and I always throw these in the bin, please don't give them to me" for them to listen. Obviously I was being a bit too subtle, but I digress.
Omega 3 is also in grass fed lamb and beef. You don't want the flaxseed oil ones, the plant-derived stuff isn't in a format that you can easily use.
And please please please don't make your offspring eat those enormous fish oil tablets, my parents tried that on me when I was a kid with these absolutely huge vitamin tablets and I hated them (too hard to swallow) and would palm them into my pocket and bin them. Waste of money for my parents - they stopped buying them when I accidentally left them in my pocket one time and they turned the wash yellow. If you're going to dose the kid, use that liquid stuff they advertise on TV. Miss 10 here is another anti-tablet kid and almost fainted at the size pregnancy/breastfeeding capsules I have here (mostly fish oil of course) and grilled us for 10 minutes on how on earth it is possible to swallow something that size
Edit: for anyone horrified at wasting so much fish and why don't I give it to someone else, I live amost a 3 hour drive away from Adelaide, and there's no way I'm going to leave a really smelly slightly leaky plastic bag of partly thawed raw fish fillets in my nice warm car for 3 hours, refreeze them and then attempt to give them away. It was easier to just dump them in the nearest public bin, my go-between never wanted them either and she said she always passed on my messages but ... I still got the fish. I don't know what kind of fish it was, just that it was incredibly strong-smelling. I have no idea what they were thinking with the fish, putting the stuff in an icecream container or anything else that didn't LEAK would have been a better idea.