actually, I also gnaw at their chicken bones eg chicken wings because I am appalled at how much meat they leave behind and I can't bear to waste it. I often get them to look at my bones (which I clean like a hyeana) and compare it with theirs, and they just try to escape.
I come from a fairly frugal family, and it didn't help that I spent part of my childhood years in a country afflicted by war and food scarcity (food rations, kinda like the WWs. DCs get excited when I tell them about having coupons for milk, and bananas and butter being a luxury). We weren't allowed to have anything left on the plate. At school, i remember we were supposed to glue two short pencil stubs together to make them last longer.
ANYWAY, I don't see the problem- we've all learned at school that we are sharing germs in a family - what is so gross about eating the leftover salad off of DD's plate? Tbh though, I only do it with my kids, not eg DH or my siblings.