I have been slowly talking to my girls, 15 and 17 (in two weeks). It's taken time and love and encouragement and consistently showing them the material. I let them watch "Fat Head", "King corn", "Frankensteer" and others. I was a vegetarian for 17 years. It's been hard for me to do a 180 and then tell them to do the same. So, Primal works, I feel better and I keep gently plugging at them. Fix them Primal Pancakes with fruit and whipped cream. Fix them Primal Muffins. Keep doing what you're doing and they will see the truth. My 15 yo loves chicken and we didn't eat it all while vegetarian. Find what works for your kids (like bacon and eggs) and feed it to them for "special occasions" and then increase the special occasions to every other day and ...
Kind of back door it, know what I mean? It's worked with mine but it does take time.
The eyes of all hope in thee, O Lord: and thou givest them meat in due season.
Freedom consists not in doing what we like, but in having the right to do what we ought.
Pope John Paul II