I used to make the kids "monster meals"; introducing foods they hadn't ever had before using their AD&D Monster manual as a guide...

crab, spinich pasta, corn beef are a few of the things I snuck in that way.

And I could almost always get something into meatballs or meatloaf if no other way.

The other thing was to meneuver them into having it in a restaurant - then they had no excuse to not eat it at home.

well - that worked until the B-I-L became self employed and torpedoed our culinary efforts by making the kids anything they wanted; he would cook three seperate meals for himself, my niece and my nephew. (Something their mom and I had refused to do.)