In a vacuum, I don't think so, no more than someone who never had a Wendy's burger because their default was a Big Mac is missing out. It's really just a different default and from a taste or "missing out" perspective is no better or worse. Though in other ways I think the impossible stuff is better objectively and subjectively.
However, in the real world (caveat: I don't have children myself quite yet), I'd personally probably be fairly loose with their defaults, let them try whatever they want, and be a good example myself of eating a mostly vegetarian diet. There will be some social pressure to have eaten a beef hamburger, for example, and I don't want them to feel like they're missing out or feeling self righteous for not having eaten beef. I think the ideal would be that they try beef hamburgers and eat them occasionally, but largely choose not to. Side note: the butcher shop I use does make hamburgers, they're super good and from ethically raised animals so I don't have ethical qualms about getting them, but also wow are they expensive. I want to say $8-10 for a patty.