Tell them a joke:
There once was a cannibal, and her kids were looking up at an airplane passing by. The kids shouted:
"Mom, look, an airplane!"
"Yes, but the content is... delicious!"
Conclusion? Eating meat is ... eating flesh. (Warning: Who wants to be a cannibal?? Or, would you mind being served for supper?)
Just trying... c'mon, make them laugh, they'll get the point better!