I became vegetarian two years ago (or just more than that). I have a six year old daughter who was raised to age 4 on meat and rice and a few veggies here and there...oh and fruit. So basically your all american 'balanced' diet. At least this is what my X felt was balanced.
In any case, when I became vegetarian, I made a concious choice to do so. But my daughter, raised until age four on meat, was not all that interested in the vegetarian diet.
She's still not vegetarian. But we have an understanding. She eats veggie at home. I don't buy or cook meat or dairy (well, very rarely I'll get cheese or yogurt for her...organic). I have let her decide which meat substitutes she enjoys the most, and whenever we eat out she can choose meat. Or if we eat at someone's house meat is an option for her. Also she's back to getting school lunch, so she can choose it at school.
I believe in setting an example for someone and showing them a good and healthy diet/way of life...but I also believe that whenever an adult decides to make a huge change in his/her life, there is something kind of wrong about expecting/forcing a child to just do what you want because you say so. My parents did this to me growing up because my Mom was just a religious fanatic and my Dad decided to move every two years. They never gave a crap how we felt about it, and we never got to choose....it took me years to go back to church at all...and I'm still annoyed with my Dad sometimes.
So, I think kids (esp since these were raised as omni) should get to be their own little unique selves and figure out over time how they want to live and what they want to eat. My daughter now always tells people that I'm a vegetarian, what I eat, why I eat what I eat, etc. So the message is sinking in and I think if I do a good job, she'll learn to make good choices for herself.
Hope this makes sense.