I have a cousin who is a PETA member.
Of course she is a vegetarian, and she feeds her two young children only vegetarian foods. She doesn't preach to any of us, so we don't say anything to her.
Now my youngest daughter's best friend (they're both 9) declared herself to be vegetarian recently. She says she "feels bad for the animals". I can respect her decision, and she can whine about it all she wants in her home, but she came into my home and tried to preach it to my kids. I put a stop to that quickly, telling her to keep that opinion to herself while in our home.
As I feared, it started rubbing off on my youngest daughter.....
Before I go any further, let me say that I eat meat, LOTS of it. We are part of the food chain, so we're supposed to eat it, that's just how things are.
So one night my daughter refused to eat spaghetti because it had meat in it. I said "Fine then, don't eat." She ate a few noodles and went to bed hungry. She tried this little protest once again about a week later. Again, it didn't work.
Finally I told her that if she kept this up, I would buy only meat products to eat, and cans of beef gravy to drink. I wasn't serious of course, but my 9 year old thought I meant it.
That was the last time she complained about meat, and she eats it as often as we do. I even have her friend eating it once in a while, when she comes over.