I throw stuff in sometimes if it's not utterly unexpected. Like I'll put shredded zucchini in my pasta sauce. They can see it if they look hard, but there's no discernible taste (even to them!) and in tiny shreds like that, there's no real textural effect on the sauce. But I often change up my pasta sauce, and they don't ask "What's in this?" very often. (When they do, it's usually because they think it's really good!) So I don't think it matters much to them.
I try not to make things too weird though. It's not worth the trust issues.
Never using recipes helps! They don't expect my food to always be the same. And both my boys say they want to become chefs when they grow up (as well as engineers, race car drivers, chemists, architects, etc., etc.), so I think I'm doing okay.
I like to play with food and try new things, so they do, too. I think that's a big key in our family. Food is fun!
And I should note that my kids aren't terribly picky eaters. I think acs is right that some kids are just easier with food than others, and no amount of tricks, cajoling or techniques will change some of those tough cases. I always feel like parents get blamed for that: those who feed their kids nothing but McNuggets from birth deserve it, but those poor parents who are doing everything they can to teach good eating and are just stuck with kids who won't eat are unfairly blamed.
